Syria's notorious Tadmur prison: Tadmur was the dumping ground for political dissidents during the Hafez al-Assad regime for three decades, and conditions inside were horrific. Built as a panopticon -- a ring of cells observed by a central guard tower -- Tadmur was a nightmare for inmates. They weren't allowed to ever make eye contact with guards, and torture was a daily occurrence. Inmates were put inside truck tires and brutally beaten on their first day, and probably the most shocking event in the prison's history came in 1980, after a failed coup. Al-Assad loyalists took helicopters to Tadmur and walked through the prison emptying machine guns into the cells indiscriminately.