The main building of the World Ocean Museum, situated halfway between the sub and the Vityaz, is home to 14 marine and freshwater tanks containing over 130 species including piranha, rays, sharks and shellfish. It's not huge by any means but is certainly well-maintained and is likely to be the main attraction for kids. There is also a decent viewing deck to take advantage of upstairs which looks out over the river, the museum fleet and up to Kant Island and the cathedral.