The volcano of Mysterious Island, Mount Prometheus, has become Captain Nemo's base. After traveling through its caverns, now guests board "Terravators" (which are elevators) to the facility's base station which is one half mile below. In the base station is a communication center which is currently giving warnings of increased volcanic activity, but the scientist who mans it is currently away on tea break.
Guests then board steam-powered mine vehicles that travel through pre-drilled tunnels into the heart of the Earth. The ride begins through a cavern of colorful glowing crystals, before entering a giant Mushroom Forest, which is inhabited by strange insect amphibian-like life forms. Before the car can proceed further, an earthquake causes a cave-in of the tunnel ahead, forcing the car off its planned route and down a side branch filled with giant egg-life sacks. The car emerges on the shore of the Subterrenean Sea, and is nearly stuck by a lightning from the electrified gas clouds. The finale comes when guests are forced into the fiery heart of an active volcano (Mount Prometheus), where the guests come face-to-face with a giant lava monster that calls the Center of the Earth its home, roaring at us for disturbing her nest, before escaping back to the surface on the wave of an eruption.
Journey to the Center of the Earth was originally planed to be a free-fall type ride as part of Discovery Mountain, which is a former Disneyland Paris concept in place of Space Mountain. There was also plans to make it an addition to the Studio Backlot Tour at Disney's Hollywood Studios when Disney was exploring the idea of adapting the book into a film, a sequence which included an encounter with a giant lava creature. When both of these concepts fell through, the project reemerged in Tokyo DisneySea in the form of a dark ride utilizing the slot-car ride system developed for Test Track.
A corporate sponsor lounge exists within the mountain with a window looking directly at the lava monster.
The lava monster's figure seems to be repurposed from the defunct Walt Disney World attraction ExtraTERRORestrial Alien Encounter where it was used for the titular alien until the attraction's closure in 2003. It is unknown if this animatronic figure was moved from the attraction or simply reuses the same moulds as the original figure however.
The giant lava monster was nicknamed as Hortense by the imagineers.