I've seen it once on a festival, at the time it came out, and I was impressed. Would love to see it again, but it doesen't seem to be published in the western Europe.
I don't remember much of it nowdays, but the main idea was that there is a forgotten underwater museum somewhere in the sea!
So the main characters go in search for it. There are a lot of horrific scenes with a great number of real mentally retarded people, and it takes some bravery to watch it, but, at the end the film can be compared to the ones of Tarkovsky.