A professor and his colleagues follow an explorer's trail down an extinct Icelandic volcano to the earth's center.

In Edinburgh, Scotland, in 1880, Professor Oliver Lindenbrook is knighted to the acclaim of his colleagues and students. When his prize pupil, Alec McEwen, presents him with a lava paperweight to commemorate the occasion, Oliver discovers that encased within the Italian lava is a rock from Iceland, halfway across the world from the volcano. After Oliver identifies some etchings on the rock as those of Saknussemm, an Icelandic scientist who years earlier descended into the interior of the earth, never to return, he sends a dispatch to his colleague, Prof. Goetaborg in Stockholm, asking him to confirm his findings. Upon learning that Goetaborg has vanished, Oliver realizes that the Swede has decided to conduct his own expedition. Now in a race to reach the center of the earth, Oliver and Alec leave immediately for Iceland and Alec bids farewell to his fiancée Jenny, Oliver's niece. Aware that they must begin their descent on the last day of May when the sunrise will pinpoint the opening into the Earth, Oliver hurries to assemble the equipment needed for his journey, but soon learns that it has all been purchased by Goetaborg. When he goes to confront Goetaborg about the situation, Oliver discovers the Swede lying lifeless in his hotel room, poisoned. Soon after, Goetaborg's wife Carla arrives to join her husband. Oliver breaks the news of her husband's death, but when he requests the use of the equipment, Carla agrees on the condition that she be allowed to join the expedition. With no other choice, Oliver reluctantly accepts, and the three are then joined by a husky Icelandic jack-of-all trades named Hans Belker and his pet duck Gertrude. As they slip inside the Earth on the last day of May, they are secretly followed by Count Saknussemm, a descendent of the original explorer. Their first trial occurs when a boulder, dislodged by an earthquake, tumbles threateningly toward them. After a narrow escape, they discern a series of notches left by Saknussemm, marking the path to the center of the Earth. Unknown to them, the count has sabotaged his ancestor's markings, sending Alec over the side of a precipice. After Hans rescues Alec, Carla uncovers the real markings, and they realize they have been tricked. Becoming separated from the rest when he follows a tunnel, Alec sinks through a bed of salt into a chamber, where he comes face to face with the count. When Alex refuses to carry the count's equipment, the count shoots at him, and the sound of gunfire alerts the others to their whereabouts. Following the echoing gunshots, the three soon find the wounded Alec and the count, who threatens them all at gunpoint. After Oliver tricks the count by throwing salt in his eyes, they accuse him of murdering Goetaborg and find him guilty in a mock trial. Although he is sentenced to die, the three find themselves unable to carry out the sentence. The Count then begrudgingly joins the expedition, and as their lamps begin to fail, he discovers a luminescent algae that renders artificial light unnecessary. Two hundred fifty six days later, Carla and Oliver are still bickering about the journey. When Alec discovers a massive mushroom forest, Carla prepares the mushrooms for dinner while the count orders Hans to chop the plants down to build a raft that will carry them across the ocean of the underworld. Just as they are about to set sail, an army of giant flesh-eating lizards appear, but they escape by fleeing into the water. Once at sea, they are encompassed by a magnetic force field which Oliver realizes is the center of the Earth, whose intense centrifugal force throws them onto shore, exhausted. As they sleep, Gertrude waddles off, and when Hans awakens, all he finds is a pile of bloody feathers. Realizing that the count has eaten Gertrude for dinner, Hans lunges at him, and when the count retreats, he is crushed by a falling pillar of rocks. The collapse reveals the sunken city of Atlantis, where they find the skeleton of Saknussemm, his finger pointing to a shaft that leads to the chimney of a volcano in Stromboli, Italy, the way out of the underground. Oliver sends Hans to inspect the shaft, and when Hans reports that it is obstructed by a giant block of stone, Oliver decides to dislodge the obstruction by using a cache of gunpowder found in Saknussemm's knapsack. The group takes refuge from the explosion in a giant asbestos chalice, but when the gunpowder fails to ignite, Oliver jumps down to relight it and is attacked by a giant scorpion. Escaping with Alec's help, Oliver climbs back into the chalice just as the gunpowder detonates, killing the serpent and destroying Atlantis. The chalice and its inhabitants are swept up though the tunnel and spewed out into the sea, where all but Alec, who lands in a tree, are rescued by Italian fishermen. The party then returns triumphant to Edinburgh, where Jenny and Alec are married. When Oliver asks Carla to stay and collaborate with him on his memoirs, she reacts with indignation at being relegated to the role of his secretary until he proposes and embraces her.