The "Kuroshio Sea" is a super-gigantic fish tank located at the Okinawa Churaumi Aquarium in Japan. It's the second-largest tank in the world (second only to the Georgia Aquarium), holding nearly 2 million gallons of water, and housing four whale sharks (the world's biggest fish), among others. The video below shows spectators watching the action, and divers are visible inside the tank -- dwarfed by the fish, sharks, and manta rays. From the filmmaker's description:
The main tank called the "Kuroshio Sea" holds 7,500-cubic meters (1,981,290 gallons) of water and features the world's second largest acrylic glass panel, measuring 8.2 meters by 22.5 meters with a thickness of 60 centimeters. Whale sharks and manta rays are kept amongst many other fish species in the main tank.