This room is represented by a red target symbol on the map - representing the circle you will find in the room.
If you go into this room whilst still alive then nothing special will happen, you will just be able to see the faint outline of the Wicca circle in the centre of the room.
If you return once your character has died and returned as a ghost then you can bring your character back to life by standing in the centre of the circle and waiting for the bar that appears to fill up. Your character will be resurrected with a random amount of health up to the value of 50 HP unless you are playing as Wizard who will come back to life with full health, even if it is above 50 HP.
After this the Wicca Room for that floor will become an empty room - you cannot use it for a second time. Wicca Rooms on subsequent floors will work as normal if you die a second time