Sumida Aquarium
This aquarium is located on the 5th and 6th floors of Tokyo Skytree Town’s West Yard area.
There's a combo ticket for the Tokyo Skytree observation decks (350m and 450m) plus the aquarium, which is a good deal. Sumida Aquarium is on the 5th and 6th floors of the Skytree. The space isn't huge, but it has the largest indoor open tank in Japan. You can see sharks, rays, and lots of Japanese marine life.