There is no antagonist in the classic sense in Journey to the Center of the Earth. The three main characters work together on their journey to overcome obstacles and defeat terrifying creatures. If you think of the antagonist as the opponent of the protagonist, then the best approximation of an antagonist would be the harsh subterranean world the men are exploring. But the physical hardships they face are just that; there is no active intelligence trying to thwart the men.

Another way to think about antagonism in the book is through the relationship of Lidenbrock and Axel. They are far from enemies, but they do serve as foils for one another. Axel is a skeptic and thinks the journey is a mistake, but he agrees to go out of loyalty and affection for his uncle. Lidenbrock, on the other hand, is fearless and determined to penetrate the secrets of the earth no matter what.

One example of this dichotomy comes after they weather a tremendous storm on the subterranean sea. Axel wants to know, pragmatically enough, how they intend to get back home, and the uncle characteristically dismisses the concern, essentially saying that something will turn up. This is not really an antagonistic relationship, however. It is more accurate to say that the professor and Axel represent two aspects of the scientific temperament.