To get here the fastest/cheapest way by train, enter your starting location into the
From the Mitsukoshimae subway station, follow the signs to the Art Aquarium, up the escalators. Sometimes there is a line (especially for Night Aquarium), so you’ll be directed to a Disneyland-like maze for waiting until there is room in the venue. The attendants with signs will tell you how long the wait will be, and in my experience, they’re pretty accurate.
Here’s more fun stuff to do in the Nihonbashi area.