The prison was built in 1908 by the French, and expanded in 1930 and 1940 to accommodate the ever growing number of political prisoners generated by the Viet Minh liberation movement.
Nicknamed 'the grinder', it was notorious for being the most miserable place in the country to be incarcerated. One observer described it as 'an open coffin waiting for dying prisoners.' Inmates reached the prison via a 13 day forced march which was designed to cull their numbers before arrival. For the ones that made it, they came to a place where malaria was rampant, and the conditions were even worse than Hoa Lo — in fact, the more 'incorrigible' prisoners from Hoa Lo were sent here to be 'ground down,' thus the name.
Of course, herding together so many revolutionaries had the opposite effect the French had hoped for. Strong Viet Minh cells formed within the prison walls, held meetings, deliberated, and communicated with their comrades outside. If a prisoner wasn't a communist when they entered, they were by the time they left. One key leader of the movement, To Hieu, who eventually died in the prison, is memorialised with signs indicating which cell was his (now mostly rubble), the peach tree which he planted (that miraculously survived the bombings) and his makeshift tombstone is on display inside the prison museum.
The museum, with a small display of photos, hand and leg irons, and the like, sits in what was a guard house sitting above a rank of underground cells below, and these have survived the bombing intact. It's horrific to imagine human beings spending years of their lives in these dank, tiny chambers. In summer, they must have been like ovens.
This place was a lot harder to escape from the Hoa Lo, partly due to the remoteness of the location, but also because of the 'incentive' program set up by the French. They made a deal with the local ethnic minorities to pay out half a kilo of salt for delivering up the head of an escapee — reminiscent of the practice of paying for scalps implemented in the French-Indian War in America.
The prison's reign of infamy came to an end during the Second World War, when France was losing its grip on its far eastern possessions. There was a half-baked plan to use the prisoners as soldiers in exchange for their release, but the transport process was mishandled, and they all managed to escape. This place is where much of the determination that lead to the Vietnamese victory at Dien Bien Phu was born, which is something to think about when you visit A1 Hill.
There's also a small museum in the People's Committee Headquarters building just behind the ticket booth. It comprises three rooms: the first room contains archaeological relics, though few are labelled in English; the second is dedicated primarily to Ho Chi Minh, with a number of black and white photos charting prominent events and some more recent colour shots; the third room is filled with the costumes of local hilltribes, although the tribal-wear on display is pretty much exactly what they still wear, and can more sensibly be viewed by simply walking down the street with your eyes open.
To get here, head west along Dien Bien Phu from the roundabout, towards Tuan Giao, and the prison is well sign-posted from the main road, 400 metres up a steep hill to the right, on Duong Khau Ca. From the park area turn off Street 26-8 at the Mini Hotel, walk up the hill and follow the sign to the left. There's a pretty informative booklet about the prison in the gift shop at the ticket booth, in Vietnamese and English, for 25,000 VND.