12: 

The beds were lined up six deep, each one with a single white cotton sheet, and a rough but sturdy wool blanket.
Each occupant had one small chest under the bed. It contained a pair of jeans, washed daily, underwear, and a plain white t shirt. No other items were allowed for the occupants own safety. A small speaker was in the left corner of this room. It was quiet now while they slept, but during the day it would play a weird haunting song of piano keys. The same song played all day from wake to sleep.
It was enough to drive anyone insane.
Outside this room was a long hallway, lights fluorescent and humming with electrical madness. And 11 other rooms all exactly the same lined the hallway.
Three attendants were tasked with keeping everyone clean, fed, and alive. Occasionally a fight would break out in a room. The attendants did not intervene. Hopefully everyone would survive and then they would change the rooms of the offenders.
The pay was too low to do otherwise. The attendants ate the same meals as those locked in those twelve rooms. They slept the same hours. 

One would have to ask, were they trapped here? In a grey building on a green hill, with twelve rooms, six occupants each,  watching the days past bye, listening to a piano play.