Kirillov Monastery
In its 17th century heyday it housed over 200 monks. Their rooms (called cells) were 8 sqm and their only furnishing was an icon to pray to. No bed, chair or desk, and with an outside loo. Now only 10 monks live in the monastery and museums take up some of the space. I think my attention span for icons is less than for Catholic Church decorations, so I've seen more than enough so far.