Nan Madol

Nan Madol is located on the island of Pohnpein, the main island of the Micronesian state of Pohnpein.

An excerpt from the article 19 facts about Nan Madol
The island is inhabited by the majority of the population of the state, about 34,000 people. It belongs to the Federated States of Micronesia and is the most cosmopolitan of the islands belonging to the federation. The island has both the state capital (Kolonia) and the capital of Micronesia (Palikir).