Based on more than 200 interviews with former detainees, including women and children, and defectors from the Syrian military and intelligence agencies, this report focuses on 27 of these detention facilities. For each facility, most of them with cells and torture chambers and one or several underground floors, we provide the exact location, identify the agencies responsible for operating them, document the type of ill-treatment and torture used, and name, to the extent possible, the individuals running them. The facilities included in this report are those for which multiple witnesses have indicated the same location and provided detailed descriptions about the use of torture. The actual number of such facilities is likely much higher.