During WWII the prison that once stood here was used by the Gestapo – that's the time period that the displays in this grimly fascinating museum focus on. Around 100,000 prisoners were held here from 1939 to 1944, of whom around 37,000 were executed. The prison was blown up by the Germans in 1944, but a mangled chunk of gateway complete with rusting, barbed wire and three detention cells (which you can visit) survive.
The prison itself dates back to 1835 and was originally built to incarcerate enemies of the Russian tsar.
A joint ticket (adult/concessions 20/10zł) covers admission here and the Mausoleum of Struggle & Martyrdom and the Museum of the X Pavilion of the Warsaw Citadel within seven days.