"Cell."

If you ever read Mark Gruenwald's old Captain America serial Streets of Poison, Bullseye guest-stars; and starts his appearance in a cell. Since he was able to turn anything into a deadly thrown weapon, even items like pens or paperclips or orange seeds, Bullseye was not allowed solid food, toilet paper rolls, utensils, or a bunk or toilet. His food was dispensed into a recessed bowl on the floor, his toilet was basically a hole, I'm not sure he was given as much as a blanket or a pillow...and yet Bullseye still escapes, because Bullseye is scary effective and surprisingly clever. Still, before he does, Gruenwald mentions the ACLU protesting his conditions, which would be cruel and unusual for anyone else, but weren't quite good enough to keep him in...

When I got the Batcave a couple weeks ago, this came to mind.