One of the various types of challenge rooms in the game. It contains a number of Feral cats and one small dog. By defeating all of the cats, you will be rewarded with an item, however the difficulty of the room scales largely depending on how many Feral Cats are in the room. Should multiple cats be present, the room will also be littered with caltrops. There is also a chance for a leader variant of the Feral Cat to spawn, which gives the player a chance at getting the achievement for defeating it.
It seems that the Crowns lesson increases the chance of a cat room appearing.