The Independence Palace, Saigon. This used to be the official residence of the President of South Vietnam, and is now a museum. A gargantuan structure sprawled over a huge ground and consisting of massive rooms used to house dignitaries and diplomats. It even has an underground bunker.
The Hoa Lo Prison built by the French and used to incarcerate political prisoners during the Vietnamese uprising and later used to house American POWs during the Vietnam war. Was also nicknamed "Hanoi Hilton" by the Americans.