Namhansanseong is a mountain fortress located in Gyeonggi Province, South Korea, just south of Seoul. It was built during the Joseon Dynasty in the early 17th century as a defensive stronghold against potential invasions from the north.

The fortress is situated on a mountain ridge and has a total circumference of about 12 kilometers. It is composed of various structures, including gates, watchtowers, bastions, and barracks, all designed to maximize the defensive capabilities of the fortress. The fortress also includes several temples, shrines, and other religious structures.

Namhansanseong was designated as a UNESCO World Heritage Site in 2014 for its cultural significance and well-preserved state. It is a popular tourist attraction and a popular destination for hikers and outdoor enthusiasts. The fortress is also used for cultural events and festivals throughout the year.