This aptly hidden attraction lies on the edge of the Thăng Long citadel complex—Hanoi’s only World Heritage Site. Known as the Military Operation Bunker General Command Headquarters, or simply as the T1 Operation Command Bunker, this relic played an important role in the Vietnam War, or the American War as it is known in Vietnam.

The construction started toward the end of 1964 to serve as the military headquarters of the freedom fighters of Vietnam. Today, the subterranean exhibits showcase artifacts from the war, such as maps and military uniforms. The site consists of tactical briefing rooms with telephones used for correspondence with President Ho Chi Minh. 

In 2013, the 40th anniversary of the signing of the Paris Peace Accords, the secret bunker was finally opened to the general public. It remains a lesser-visited, under-appreciated attraction in the medieval citadel complex.