The building went up between 1904 and 1906 and was, for its moment, advanced - electric light throughout, steam heating, 157 cells with room for 203 prisoners. It was built as a court prison, for people awaiting trial or serving short sentences, and it sits inside a working legal complex to this day - police headquarters and law courts still occupy the ground to the south, east and west, which is why visitors enter from the north, off Weigangstrasse. When the Stasi took it over in 1956, the architecture barely changed. The method did. Isolation was the point: prisoners kept apart from one another, watched through cameras, listened to through microphones, reported on by informers placed among them. Around 150 people were held at a time; the peak came in July 1962, at 260. Renovations in the 1970s brought better heating, washbasins and toilets into the cells - improvements measured in plumbing, while the silence stayed exactly where it was.

The same corridors served four different states, and each one used them for its enemies. Under the Kaiser and then the Weimar Republic it was an ordinary court prison, at its most lenient between 1923 and 1933. After 1933 the cells filled with political prisoners, communists above all, and from 1939 with resistance fighters captured in the countries Germany had occupied. The Soviet occupation authorities kept it as a political prison from 1945 to 1949, its most crowded era by far - as many as 400 people in a building designed for half that. The Saxon judiciary ran it briefly in the early 1950s. Then, in 1956, the recently formed Ministry for State Security took the keys and did not give them back for thirty-three years.

Georg Dertinger had been the GDR's first foreign minister; he was held here from 1956 to 1964. The philosopher Wolfgang Harich, who had argued that East German socialism needed reforming, arrived in 1959 and left in 1963. The novelist Erich Loest, convicted in 1957 of "counter-revolutionary group formation," served seven years in Bautzen and was forbidden to write throughout; in 1991 he published a memoir about being permanently overheard, titled after Goethe's secretary - Die Stasi war mein Eckermann, my life with the bug. Rudolf Bahro was here in 1978 and 1979. From 1963, a wing on the first floor held women, never more than nineteen at once. The Raufeisens came as a family: Armin, sentenced to life for espionage, his wife Charlotte to seven years, their son Thomas to three, all three inside the same building and unable to see one another. Thomas was released in September 1984. Armin died on 12 October 1987 in a prison hospital at Meusdorf near Leipzig, after gall bladder surgery. The official cause was recorded as pulmonary embolism. The circumstances have never been explained.

In thirty-three years of Stasi control, one person got out without permission. Dieter Hötger escaped in 1967 and was free for nine days before he was recaptured. The number sounds like a footnote until you consider what produced it: constant observation, cells that isolated, sentences calibrated to frighten. People convicted of helping others flee to the West were given fifteen years as a matter of deterrence - a punishment aimed less at the person in the dock than at everyone who heard about it. Deterrence was always what Bautzen II manufactured. It worked best when nobody had to be sent there at all.

The last political prisoners walked out by 22 December 1989, six weeks after the Berlin Wall opened and ten months before the two Germanys became one. A handful of ordinary convicts, never more than twenty-three, stayed until the prison shut completely in January 1992. Then came the argument about what to do with the building, and the decision that makes it worth the trip: keep all of it. Since 1993 it has been a memorial and museum, most of it untouched - the central stair, the corridors, the cells, the punishment cells, the exercise yards with their concrete table-tennis tables. Admission is free. Outside stand the vans that brought people here without letting them know where they were going. In the north of town, on Talstrasse near the still-operating Bautzen I - the penitentiary the GDR nicknamed the Yellow Misery - lies the Karnickelberg, a burial ground for prisoners who died of illness or of beatings, mostly during the Soviet years. It opened to the public in 1990, and a chapel followed in 2000 to tell visitors who the dead had been.