Black Site Prison

You have committed (insert your crime here) and are thrown into the back of a van with a bag over your head. You wake up in a black site (unsanctioned government jail) prison cell. You are told you have an hour before they transfer you to a maximum security prison, from which it will be impossible to escape. Pacing your cell, you notice marks on the wall and realize there might be a way to get out before they transfer you. Time is ticking...