Greece, February 2023

When I was in Thessaloniki it was somewhat out of the main tourist period, so I didn't expect to do anything exciting there. But at least there were some things to do (albeit rather relaxed activities) and for about half of them, there are no pictures to show. It still was fun, though. And a museum turned out to be more interesting than I had expected.

I had been looking for something to do during the two days I had available, but a lot of activities only happen in springtime or summertime. However, there was a rafting tour available on Nestos river, which is about 200 km from Thessaloniki. I had a car available, so I thought: Why not?

Getting ready for rafting Getting ready for rafting Getting ready for rafting

As an activity, it was rather calm. The Nestos is a wide, slow running river without any rapids or tricky sections.

Nestos river

Which meant that we were mostly paddling along and enjoying the view.

Nestos river Nestos river Nestos river Nestos river

Even though it looks a bit drab on the pictures (there had been a forecast of rain, which fortunately happened only two days later, but it meant that the skies were overcast), the area looks great. The river runs through a gorge, with an impressive rock wall on one side.

After a while we went down a die branch of the river.

Nestos river side branch

Technically not so much a branch or distributary, but more the bit of the river that runs on the other side of an elongated island in the middle.

Doesn't matter much, though.

It was different from the main river, a bit smaller and with more vegetation hanging over or into the river.

On other side of river island On other side of river island

It also had a bit more wildlife (though, admittedly, the heron would also have been visible from the main river, although we would not have startled him there sufficiently to break into flight.)

River turtles Silver heron Silver heron

Besides the rafting, there was also a zipline across the river. And another one back again.

It wasn't particularly long, but it was fun to do.

The only downside was that you had to walk up rather rocky terrain to get to the starting point on both sides.

Going to the zipline starting point

Then you reached a wooden platform from which you made your way across the river (with a couple of people hiking to a viewing point on the path below).

Starting point seen from zipline

While being over the river, you could spread out a bit. But that was only for about five seconds or so, before the line went through some trees and bushes and we were asked to curl up a bit tighter there. (As usual, this presumably wasn't necessary. All vegetation had been trimmed back that you couldn't have touched it, however far you tried to reach out. But approaching the 'tight bits' from the open stream, it looks like a small opening, so you kind of automatically pull your arms and legs in anyway.)

Heading into the hedges

On the other side of the river is another short, but steep ascend to get to the second zipline.

Way to second zipline

Inversely, you start out going through some somewhat tiny looking (see the little stripe to the right of my hand in the next picture - that one) and then you cross the river to arrive back where you started from.

Looking back to second start point

And then there's the short bit across the river, where you can (kind of) spread out.

Almost back at the start

(As usual, I am a bit surprised at how concerned I look. I like ziplines and enjoy them. But that never seems to show on pictures.)

After riding the zipline a couple of time, I drove up to a sightseeing point higher up in the mountains and had a look at the gorge from there.

Nestos Gorge

Due to the weather, the pictures are a bit disappointing. The view, however, was great. And the crinkly, serpentine road up to the sightseeing point was mostly deserted and fun to drive with the small car I had rented.

Not the moi st exciting day ever in Greece, but I did enjoy it.

I spent most of next day driving to caves.

I went to visit Alistrati cave and Aggitis cave, but both have rather strict 'no photography, no videos' policies, so there's not much to show here,

Both caves were interesting.

Both of them have been discovered rather late (Alistrati in 1975 and Aggitis in 1978), so they escaped a lot of the vandalism that other caves, discovered in earlier times, had to endure.

So most of the formations are still intact, with none of the "this nice stalactite will look great above the fireplace at home - so I'll saw this off and take it with me" that plagued caves discovered a century earlier.

Alistrati has the larger variety of formations, including a couple of unusual ones (besides a lot of stalactites and stalagmites). There are 'brushes' of calcite coming horizontally out of the rock, which are rare, but there is also 'cave popcorn', according to Wikipedia "small, knobby clusters of calcite".

The do look a lot like popcorn. So much that I felt a bit tempted to go to a supermarket, buy some popcorn, and put some in my hand. And when the guide talks about how much it looks like popcorn, I could reach out, pretend to break some of the wall, but it in my mouth, chew it and state "Yes, tastes like it too."

The is, admittedly, childish and would probably get me banned from cave visits by the Hellenic Speleological Society, but it might be worth it. Maybe next time.

Alistrati also suffers a bit from well meant technology.

They have their cave lights on a timer, so when a group of visitors follow a tour, they have only a limited time on any spot until the a spot a bit further down is lit and the current spot gets dark again.

Which is a reasonable approach to keep the group moving, bit has some shortcomings if somebody asks a follow-up question and the timing is thrown off. Then there's some stumbling in the half-dark.

And it isn't helped by the second 'helpful' addition, a 'robot guide' named Persephone, that feels like an ambitious idea that was realized a bit too early.

Persephone is an autonomous moving robot that can present the cave in 33 different languages.

Seems like a reasonable idea, as this allows customization of the tour for non-Greek speaking visitors. And it also might help the quality of the presentation, as most guides sound a bit monotonic, after doing the same descriptions eight times a day, five days a week for years and years,

A decent recording by native actors who have to do it only once, while there's still some feeling to the presentation might be a good idea.

In principle.

In real life, however, even though the speeches are recorded, they come (probably intentionally) across in a sort of dull, lifeless 'robot voice', which fits the character, but defeats the point. (But maybe it was only the English version that was that dull.)

So Persephone is mostly an MP3 player on wheels.


So far.

Where the idea is starting to break down is that the robot is not synchronized with the light.

If there are only Greek visitors, it's presumably fine and the timing works.

But if they also switch on a second language, then the presentation lasts about twice as long and the lights start going off towards the end of the speech. If there are visitors with five different languages, they ae likely to see little of the cave except for the initial bit and some receding lights in the distance.

And once Persephone start moving, she does do that slowly, about the speed of a autonomous vacuum cleaner.

What makes it worse is that Persephone has about the same ability to deal with obstacles (i.e. visitors).

When the robot guide talks, visitors tend to stand in a circle around it.

And when it starts to move, there is no open path and the bot can't deal with it.

Obviously there are sensors to keep the bot from colliding with people, so the robot stops and does not go anywhere.

Until the proper guide (the human one) asks people to get out of the way and clears a path for the robot.

So, ultimately, what the advanced robot cave guide does is to play some audio files, screw up the lighting sequence and create additional work for the human guide. And look stupid.

It doesn't do it for long, though.

Well, it continues looking stupid, but it doesn't guide much.

For some reason, it can only handle the first 50 meters or so of the cave, so it only gives explanations about three 'stations' before returning to the starting point and getting ready to annoy the next group.

The job would have been better handled by three loudspeakers at those locations.

Or, if someone wants to build a robot, with a robot that runs on rails on the handrail next to the path. Not much value as a test for autonomous navigation, but not that much of a failure either.

What would have been interesting would have been a bot that could actually handle crowds in some way.

While it would be hard to do with a humanoid looking bot, I wonder what would be possible with a Boston Dynamics style robot dog like Spot.

Much more agile than Persephone in any case, but a 'dog' with reasonable sensors could try to make its way through a crowd of people by politely nudging its way through and gently pushing against the legs of people standing in the way.

I think it's likely that people would respond to that and let the 'dog' through if it shows a clear intention on where it wants to go.

And that's the nice variant.

I wonder whether there could be other dogs (slightly more sinister looking - maybe painted black, while the 'guide dog' could be yellow) follow the group and 'herd' them forward, making sure nobody stays behind or gets separated from the group.

Obviously they should not be allowed to harm people (probably), but I think that posture and body language goes a long way to make people go away. From the simple 'I am standing here, so you may as well go somewhere else' that border collies specialize in to a rather more aggressive 'Rottweiler looking at Magnum' posture for people who still don't get the message.

(The last idea kind of implies that the bots should be called Zeus and Apollo, but given that it's a cave and there are three of them, a better collective name for the three of them may be Cerberus.)

In any case, back to the cave...

The Persephone seemed like a silly idea. Someone probably made a project proposal, it got accepted, they then realized that they really needed to built it and then everyone found out that it was a stupid idea. I expect they'll keep the robot going for a bit, but if it ever breaks down and is sent for repairs, I don't think it'll ever be back.

The cave seems to be a regular victim of well meaning technological developments.

Along the way, there were a number of signs with QR codes on them.

Essentially a good idea.

Sometimes museums have them and you can get additional information about artworks or videos showing cultural artefacts in use.

Or, and here's an idea that might have been useful, sometimes they are linked to audio files, so that visitors who don't speak the local language listen to an description an a language they prefer.

Works better than a robotic guide, especially as everyone can hear their audio files in parallel, so it doesn't mess up the timing, whether there are two languages needed or ten. And everyone only hears their version, so people don't have to stand around and wait while they listen to the same information in languages they don't understand.

Assuming, of course, that visitors have a smartphone with an internet connection.

Which is precisely what they don't have in the cave.

There is no WiFi in the cave and being below a dozen meters of rock means that there's no phone signal either.

I had been wondering about that and asked the guide what the purpose of the QR codes is.

It turned out that there is an app that gives you additional information about various bits of the cave. But you need to download and install it before you enter the cave.

Which seems like a good idea - if they would tell you about it.

Admittedly, I didn't have time to hang out near the entrance for a long time before going on the tour. Essentially I bought a ticket and got told "You're with that group over there. Tour starts in a minute or so."

Which is nice and quick service, but if there had been a giant sign "Download our app now to have a better cave experience" I might have missed it.

But I did have a look after the tour and didn't see any obvious hints.

Maybe it is printed in the attraction brochure or bus tours tell people to download the app while they are on the way to the cave, and I was unlucky to miss it because I nether found out about the cave by brochure nor went there by bus.

I also looked at the official web page and (initially) didn't find any reference to the app.

It turns out that there's only a link from the Greek pages that leads to the app and there's no way to learn about it from the English sections of the web page.

Which is ok if the app is only available in Greek (though localization for different languages is something that apps support really well).

But it's not a link to an app store, but a direct link to an APK file that you are supposed to download and install on your Android device. Which, from a security point of view is pretty much a 'never do that' thing.

So while the 'app reads QR codes in the cave' is essentially a good idea, nobody seems to know about it (I didn't see any of the Greek visitors to the cave point a phone at the QR codes either) and that's a a good thing, because if people knew, it would be a risky idea to install the app.

And that's the technical side of it.

The other thing is that it undermines the rule about 'no photographs'.

It seemed that visitors respected that. I didn't see anyone pull out a smartphone and stealthily photograph a couple of stalactites. (Of course they might have easily done that so secretly that nobody noticed, but that's not the point. It's about people not noticeably taking out their phones.)

But if there are QR codes, you need to have your smartphone out and the camera on.

Which makes it much more likely that visitors take the opportunity to take a couple of pictures of the cave as well. And guides can't simply tell people to put their phones away, as (with the QR codes) they all suddenly have a legitimate reason to have their phones out.

It all feels silly and not thought through.

But the cave is impressive and quite nice. Well worth a visit.

It would help if they kept badly conceived technology out of it.

From there, I drove to the Aggitis cave.

They had the same strict rules about photography and repeated them during the tour, so no pictures from this cave either.

At least they didn't play around with fancy technology, but simply used a human tour guide.

The cave is a bit unusual, as it looks like it would look in a movie, which is mostly how real caves don't look.

It's because it has a river running through it.

Which looks cool in movies, but in real life underground rivers are a rare thing.

And here's one that also has stalactites, which means that the average water level must have been low for a long time for them to form.

Stalactites over a river look amazing. Especially well preserved ones.

But, alas, no pictures.

The only area where photography is allowed is a larger cave where the river comes out of the caves system behind through a small opening.

Part of the wall of the cave had fallen down a long time ago, so this part was always known to the locals (and as it has a lot of natural sunlight, there's no restriction on photography).

The big water wheel on the right side was never part of a mill, but has always been a water wheel with the purpose to lift part of the water further up, so it could travel further along man-made channels to nearby houses and fields.

Exit area of Aggitis cave

On the way back from the caves I passed through Serres. The town happens to be the place where the only properly certified racing track in Greece is located.

I didn't get to see the track itself - when I got there, they were already closing the gates. But the go-kart track was still open, so I did some karting there.

Of which I also have no interesting pictures, so here's a picture of the track sign and some parked karts instead.

Serres go-kart track

At least there's a GPS track of the rounds I've been making there.

The layout allows a variety of possible courses for the go-karts. When I as there, they had set up the shortest possible route around the circuit. Not much variety, but a good way to learn the proper way through the corners involved, as you go through them a fair number of times.

Serres go-kart track GPS track

I didn't intend to do any more touristy things in Thessaloniki, but on he last evening there I walked by the Museum of Illusions and decided to have a look.

I hadn't expected much. Many optical illusions, like the 'which line is the longer of these two' or 'are these lines straight or bent' effects work well with looking at a book or a monitor, so there's little to be gained by printing them on a poster and sticking them to a museum wall.

And while they had a couple of these kind of illusions on the wall, they also had a sufficient number of larger three-dimensional illusions, often involving mirrors, which you can't emulate on a computer screen and make a visit to the museum worthwhile.

And, quite differently from many other museums, they not only allowed photography, but encouraged it to the extend that the museum guides would take pictures and pose in illusions that needed more than one person to work, like this 'tall side / small side' illusion room.

Tall and small illusion Tall and small illusion

Or this 'double illusion' chair.

Double illusion chair

One effect is, of course, that the chair is larger and further back then it seems, creating the look that I'm not even hobbit sized.

But while it could have been done with a real chair, the chair itself does not exist, but consists of a mat on the floor and some wooden posts standing on the right places on the floor.

An angled mirror allows you to play poker with five copies of yourself.

Poker with myself

Unfortunately I didn't quite think it through how it would look like, otherwise I would have tried to create a better interaction with myself.

Someone else had some cards held loosely in their left hand around shoulder height, with the hand half open and then threw some cards at the mirror with their right hand. It then looked like every copy of him was throwing cards at the version to the right, while casually catching the cards from the version on the left without even looking.

There would have been a number of ways to stage a good scene, but I didn't think of any on the spot.

There's also an infinity room at the museum that works on the same principle, but is fully enclosing you, so that you have copies of yourself extending in all directions.

It's unlikely that I'll ever have a house where I can build a shower room to my own specifications, but if I ever do that, I would love to have it built like that...

Other 'mirrored things' were the kaleidoscope and the head on a platter illusions.

Kaleidoscope of me My head on a platter

The kaleidoscope looks unexpectedly neat, but the head on a platter is a bit obvious.

Of course, it's an obvious illusion anyway.

Everyone will immediately know how the effect is done in any case, but it would have been a good idea to hide the lower end of the mirrors a bit better. (Cropping the picture might help as well, though.)

They also had built two 'down is up' optical illusions.

One has you 'falling down' a vertical pipe.

Upside down a pipe

(Although the effect might have worked better if they had put the texts upside down as well.)

The other was a whole 'upside down' subway train compartment.

Upside down subway Upside down subway

For this one my posing worked better than I expected, albeit due to an unexpected reason.

When we did the first photograph, I noticed that my hair was a bit of a giveaway, as it was still pointing 'upwards', which looked wrong.

So I asked the guide to take a second picture, in which I moved my head backwards and then tried to swing it quickly forward for the picture (in a kind of shampoo advertisement style), so my hair would be thrown upwards and, once the photo was rotated, it would look pointing 'down' at the 'floor'.

It turns out to be surprisingly difficult to move your head in a way that makes the hair fly up above your head (mine 'sloshes' along the side of my head instead), bit at least it looks a bit more disheveled and less obviously pointing the wrong direction in the first picture.

But what 'sells' the illusion is that, while trying to do a 'headbanger picture', my shirt slipped out of my trousers. And that indeed looks a lot like gravity is pulling it 'down' while I am doing a handstand.

The best illusion they had was one that I didn't photograph, because it only works with movement. And even a video would not properly convey how it feels like being there.

It's a 'vortex tunnel'.

In essence, it's an elevated path going through a tunnel. But the walls of the tunnel are rotating.

Your eyes tell you that you are falling sideways, so you automatically compensate for it and lean the other direction.

(It was also interesting in terms of priority of the senses. Conceptually, your sense of balance should tell you that you are standing upright. But the moment you open your eyes, the sense of vision wins and the body ignores the little sensors in the ear and goes with the visual evidence.)

I walked back and forth in the tunnel a number of times and even if you work hard on ignoring the rotating walls and on walking straight ahead (and ahead straight), it is difficult to do so.

And once you think you got it under control, you turn around and almost fall over.

Because then the rotation seems to go the opposite way. It becomes obvious that you didn't manage to ignore the moving environment, but that you only compensated for it by 'leaning' the opposite way by a proper amount. (At least that is what the body thinks it does. In reality it simply stays upright.) And when you turn around, it adds that 'leaning' to the effect it sees, so you get 'thrown' into the other direction twice as hard as before.

It's a very strong effect.

I've been in such a tunnel once before, but that was in a moving vehicle (I think it was some part of a tour at Universal Studios), so you have the effect of tipping over, but if you are standing there and trying to walk from one end to the tunnel to the other on your own, it is much more intense.

All in all, it was a much more interesting museum to visit than I thought it would be.

After that, some good dinner at a Crete speciality restaurant (no pictures from that, though) and home the next day (at least for me - my luggage spent another two days somewhere before it got there).

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