Max Anderson (Jean-Michel Paré) is being pursued by a Giganotosaurus when he finds a fissure vent. When he tries to jump across, he falls while calling out his brother’s name. Ten years later, Max’s 13-year-old son, Sean Anderson (Josh Hutcherson), visit Max’s brother, volcanologist Trevor Anderson (Brendan Fraser). In a box of items that belonged to Max is a book, Journey to the Center of the Earth by Jules Verne. Notes written by Max are found inside the book.
In Trevor’s volcanology laboratory, a device shows activity on Snæfell, a dormant volcano in Iceland. Trevor and Sean travel to Iceland to investigate. They try to contact Icelandic volcanologist Sigurbjörn Ásgeirsson, but instead encounter his daughter Hannah Ásgeirsson (Anita Briem) since her father had died some years earlier. It turns out that Sigurbjörn and Max were both Vernians, a group of people who believe the works of Jules Verne to be fact and not fiction.
Hannah offers to help them climb the volcano. While the group is hiking up the volcano, a lightning storm forces them to take shelter in a cave. The cave entrance collapses, trapping them in what appears to be an abandoned mine. The trio then rides on out-of-control mine carts, in which the tracks start to branch off in three ways. Hannah and Trevor save each other from dead-ends and Sean reunites with them. They reach the bottom of a volcanic vent, but the floor of the vent breaks, and they begin to fall towards the center of the Earth. The vent eventually becomes a water slide which drops them safely into a lake in the center of the Earth, which turns out to be a completely separate world contained within the Earth.
The group starts seeking a way back to the surface. Along the way, they find evidence that someone had been there a hundred years ago. Trevor remarks that some instruments found are Lidenbrock’s (the name of a character in the book), suggesting that another group had previously made the journey, somehow returned to the surface and recounted the tale of their adventure to Verne. They find some of Max’s things as well. While Trevor and Sean are examining what they’ve found, Hannah finds Max’s body. They bury Max on the beach of the underground ocean and Trevor reads a letter to Sean found in Max’s journal. Trevor discovers that his brother died due to dehydration because of hot magma surrounding the center of the Earth.