Read in Japanese
You may have heard a lot about the Kaiyukan; everyone seems to want to go there. I think it lived up to its reputation, and recommend a look, but it is quite expensive (2000 yen). I enjoyed the way the exhibit was set up, with the tanks extending through different levels. If it`s too crowded in one area, you may be able to descend a floor and see the same creatures there.
The gift shops were also really nice. They have little shark forks and everything. I recommend the sweet pins.
Besides that, it`s has a wonderful view over the bay, the building itself is quite cool, and there is a ferris wheel and butt-load of shops and restaurants right beside it (the area is called Tempozan Harbor Village).
|The buildings and murals were amazing...|
|...as was the view|
The ferris wheel costs 700 yen to ride, and I can`t say if it's worth it since I didn`t go myself, but the restaurants were a nice end to our sea exploration. There was curry, burgers, ice cream, yakisoba, gyuudon... You should be able to satisfy your appetite. There were also clothing shops, a ninja store (really), and more.
The aquarium is only about a five minute walk from the nearest station. A great place to spend half of your day!