Hoan Kiem Lake (also known as Sword Lake) is located in the city center, connected to the Quarter built by the French more than a century ago.

Located in the center of the lake is the Tortoise Tower, which was built in 1884 – 1886. The tower has three floors and a top, with four sides, 6.28 meters long.

Also, on the lake, there is the Ngoc Son temple which is located on the island of Ngoc Son. The temple is connected to the shore by the The Huc Bridge.

The lake has an area of approximately 12 hectares. Previously it was known as the Luc Thuy Lake (because the water is green all year round), Thuy Quan lake, Ta Vong and Huu Vong. Hoan Kiem first appeared in the 15th century associated with the legend of King Le Thai To returning the precious sword to the Turtle God.

The lake name is also the name of a district and a street in Hanoi center. Looking from above, the lake is less than 3 km from the Chuong Duong Bridge and the Red River.

About six centuries ago, based on the Hong Duc map, the majority area around the capital was water. Hoan Kiem Lake used to be a distributary of the Red River, which flew through the city's today streets of Hang Dao, Hai Ba Trung, Ly Thuong Kiet, and Hang Chuoi. 

Since the liberation of Hanoi, the lake has become the city center and the symbol of the capital city.