Guests board a small submarine developed by Captain Nemo and participate in a tour to explore the world under the sea. This submarine was remotely controlled from the control base where Captain Nemo was, and it should have been secured by that. However, when he tried to make the submarine levitate, the submarine was attacked by the Kraken and lost control, resulting in a detour into an unknown world.
The place where the guests end up was a world of Atlantis where mermen live. They had evolved their own in a place close to the center of the Earth. The submarine was boosted by the mysterious power of the mermen, and was able to return to the base safely.