@Rhino00 Thanks for the ID! I wasn't expecting one anymore. I don't exactly remember the location. It was either in the Mediterranean section or the coral reef section above it, so when exiting the elevator to the left (and then the tanks on the far side).
@Rhino00 Good luck. There was only a single one of them on show, but it was hard to miss. It already looked like a special species but is indeed very rare in captivity.
@lintworm Yes! The day before the visit I found a photo from a visitor, so I knew it is in a lobster aquarium. It's very dark aquarium, but I managed to get a photo.