The best two aquariums I’ve been to in Japan are the Kaiyukan in Osaka and one in Okinawa. Not sure which I’d say is best, but the Osaka aquarium is very cool.
You start by taking a long escalator ride to the top of the building. The general layout is a giant central aquarium with a walkway winding around it. Making its way around several times before reaching the bottom. The central aquarium represents the Pacific Ocean and increasing depths reveal different kinds of fish. Probably the main attractions are the Whale Sharks and Stingrays. As you make your way around, looking outward from the central tank you’ll find many other fish and animals presented.
It is a well spent afternoon. Next door is the Tempozan Marketplace, mall with all varieties of food…and Legos.
It is the most unique aquarium I’ve been to.
In the one in Okinawa, the dining area is next to a large tank with the tabled butted right up next to it. While you’re eating a big shark can swim right next to you. They also have a shark feeding show that is impressive. But my favorite is in Osaka because of the very deep central tank and how you explore the layers and see the creatures at different depths.