There are hidden chests in some of the normal rooms. A simple graphical guide to the ones I've found so far.
Random room 1
Random room 2
Random room 3
Random room 4
Random room 5
Random room 6
Random room 7
Random room 8
Random room 9
Random room 10
Random room 11
Random room 12
Random room 13
The chest is hidden in an alcove in the lift shaft.
Random room 14
Chest is at the top of the room, can't miss it.
Random room 15
Random room 16
