On the first floor of Aquas, there is a really big tank called the Sea of Myths. The reason why it was named so is because a lot of Japanese myths originated in Shimane. There are many varieties of sharks, and some other sea creatures such as rays, a huge sea turtle and so on. And there are some benches! If you are tired or watch it for a moment, these benches are great. You can sit down and enjoy watching the sea creatures. If you bring kids, point out the UV lights on the back wall of this area; they might enjoy seeing light-coloured clothing glow in dark.
After the shark tank, you can walk through the shark tunnel. You can enjoy watching their stomachs, and signs of the wall tell you how to differentiate male and female sharks.
If you book the "backyard tour"–a kind of behind the scenes look at the aquarium–in advance, you can see inside this tank from the top. They also do sleepovers at the aquarium for parents and kids in the summer vacation. Check the details on their webpage.