Human rights groups say on average, 300 people died in Syria's prisons every month during the worst of the conflict. An analysis between 2011 and the end of 2015 suggest that 18,000 prisoners have died, many after enduring torture. Some of those were imprisoned simply for protesting the regime. TRT World's ''Off the Grid'' programme has gained rare access to men and women who survived years of torture inside Syria's prisons. And a warning, some of the images in this next piece, are disturbing.