At the end of the famous sea bridge in Sellin you can find this under-water attraction. It is…read morebasically a mini movie theatre/aquarium that goes 4.5m under water. My little kids liked in particular the phase where we moved into and out of the water but at the bottom we saw absolutely nothing - neither the sea floor nor a jellyfish or anything. The guide seemed to be prepared since he professionally filled the void with a lot of interesting facts on the baltic sea. Then we watched a 3D film on the animals of the baltic sea and learned a bit on what fish to eat or not in the nearby restaurants. The guide was really kid friendly - he offered the little kids to sit in the big panorama windows and on the floor in the first row to watch the movie. Overall time went by very quickly but it was too bad that we didn't see any wildlife (but then again, that's probably humanity's fault in the first place). Still, a discount on days with bad visibility would be nice.