Nan Madol is an archaeological site adjacent to the eastern shore of the island of Pohnpei, now part of the Madolenihmw district of Pohnpei state in the Federated States of Micronesia in the western Pacific Ocean. Nan Madol was the capital of the Saudeleur Dynasty until about 1628. The city, constructed in a lagoon, consists of a series of small artificial islands linked by a network of canals. The site core with its stone walls encloses an area approximately 1.5 km long by 0.5 km wide and it contains nearly 100 artificial islets—stone and coral fill platforms—bordered by tidal canals.

The name Nan Madol means "within the intervals" and is a reference to the canals that crisscross the ruins. The original name was Soun Nan-leng (Reef of Heaven), according to Gene Ashby in his book Pohnpei, An Island Argosy. The ruined city is one of today's great archaeological enigmas and is sometimes called "Atlantis," the "eighth wonder of the world," or the "Venice of the Pacific".