Across the bay from Tokyo Disneyland you will easily spot the distinctive glass dome of the city's largest aquarium. Located in Kasai Rinkai park, this government-run aquarium is an inexpensive alternative to some of the city's flashier sea parks while still being quite impressive in its own right.
The exhibits each focus on sea life from a different environment: the Atlantic, Indian Ocean, the Caribbean and an extensive exhibit on the local Tokyo Bay. In the watery blue depths you'll encounter giant spider crabs, deep sea isopods, hammerhead sharks and more. There's an enormous theater-style tuna exhibit. Outside of the water you'll encounter a waterbird sanctuary featuring puffins and a fun penguin exhibit. The park is also home to Japan's largest Ferris Wheel.
The aquarium is located 5 minutes on foot from the JR Kasai Rinkai Koen Station. Take the Tozai line and get off at Kasai Station or Nishi-Kasai Station. You can also take the Tokyo Mizube line.