Thanks for the interesting response. I love the idea of a cell. Having one can be so versatile for longer sessions. While I'm not into the whole institutional/jail vibe the idea of a small (saw 3x5 or 4x6) closet sized cell with a light proof steel door is very hot. Adding restraint points so a sub could be left standing, kneeling or prone is a great additional touch.

There was a Domme in Toronto who used a coldroom built out under the front steps of her bungalow and accessed from her basement dungeon for this purpose. Cement walls, floor and ceiling with a heavy steel door.