Disappointed not to find any information on the Citadel in Hanoi (also called Thanh Long Citadel and not to be confused with the one in Hue) on Travelfish's Hanoi attractions page, I hope that forum users can give an update: is the place now (end November 2012) open to visitors or not?
Potentially, it's one of Hanoi's top sights -- mixed in with remnants of the pre-1800 imperial palaces are archeological excavations and the command post/bunkers from which the North Vietnamese General Staff monitored their ultimately successful offensives against South Vietnam circa 1973-75.
The Citadel area was opened to the public for a while during the Hanoi 1000th anniversary celebrations in 2010 and since then there have been sporadic reports that it has been or may soon be reopened to visitors. There are also frequent posts to the effect that admission has been denied -- though it may be that folks are simply trying to get in the same door.
All in all, it sounds like the classic tussle between the national tourist authority (trying to make Vietnam accessible) and the internal security agencies (trying to keep things opaque). So, can anyone tell me what the current situation is re access to the Citadel?
As far as I am aware, it is not open to the public. This is why it's not listed in the sights section or this site. However, I will make it my mission to investigate this further and will update when I can.
After making a few inquiries, I confirmed that the Hanoi Citadel is open to the public five days a week from 08h30 to 11h30 and from 13h30 to 16h30. It is closed on Monday and Friday.
It's a nice, park-like place with absolutely no touts and still just a few tourists. Must-sees are the Imperial front gate and the smallish building where the Politburo and PAVN general staff planned the final (1975) offensive of the civil war with Hanoi's southern rival.
The place is called Vietnamese the 'Hoang Thanh,' and its public entrances are off Hoang Dieu Street. If that's too challenging for your cab or motorbike-taxi driver, just have him drop you at the Cot Co (Flag Tower) on Dien Bien Phu Street, walk west to the next corner (Hoang Dieu) and then north for about 50 meters.