The Radisson SAS Hotel in Berlin is home to the largest cylindrical fish tank in the world, standing at a whopping 80 feet tall and containing 260,000 gallons of water. It's got 2,500 fish inside that are spread across 56 different species of underwater dwellers, and you've gotta assume that it's a real pain to clean. In fact, two full-time divers are on staff to keep the aquarium clean and the fish happy.
If you want to get up-close and personal with the fish, there's a glass elevator that goes up the middle of it, providing views of the fish the whole way up. If you want a more long-term view of the fishy festivities, you can book a room that looks out into the aquarium for around $375 a night.