Go down into the bunker where the war was actually run
Nine metres down, 60 cm steel doors
A low concrete building in the citadel grounds with a stairway descending to a sealed underground meeting room, its map boards, telephones and chairs left as they were, reached through steel blast doors.
Why it's unique
Inside the citadel is House and Bunker D67, the command post of the Vietnamese high command. The bunker sits nine metres underground behind reinforced doors two-thirds of a metre thick, and the decisions made in these rooms include the 1968 offensive, the negotiating position for the Paris accords and the 1975 campaign.
It is preserved with its original furniture, and it sits on ground that has been the seat of Vietnamese power for something like thirteen hundred years. The rooms were closed to visitors for most of their existence and have only recently opened.
Before you go
Most visitors spend their time on the excavated archaeology across the road at 18 Hoang Dieu and leave without finding D67 at all. It is behind the Kinh Thien palace foundations, and the stairway down is not obvious until you are standing at it — ask if you cannot find it.
Take a layer. It is markedly colder underground and the air is still. The surface exhibition holds several hundred documents and photographs with audio commentary; the bunker itself takes only a few minutes but is the reason to come.