Niels Klim's Underground Travels is a satirical science-fiction/fantasy novel written by the Norwegian–Danish author Ludvig Holberg.

His only novel, it describes a utopian society from an outsider's point of view, and often pokes fun at diverse cultural and social topics such as morality, science, sexual equality, religion, governments, and philosophy.

Holberg knew that the satirical content of the novel would cause an uproar in Denmark-Norway, so the book was first published in Germany, in Latin, as Nicolai Klimii Iter Subterraneum.

He thus captured a broader audience than he would have gotten in his homeland.

The novel brings him wide acclaimed across Europe.

Danish, German, French, and Dutch translations are also published in 1741.

The book is significant in the history of science fiction, being one of the first science-fiction novels in history, along with Johannes Kepler's Somnium (The Dream, 1634), Cyrano de Bergerac's Comical History of the States and Empires of the Moon (1656), Jonathan Swift's Gulliver's Travels (1726), and Voltaire's Micromégas (1752).

It is also one of the first science fiction novels to use the Hollow Earth concept.