Minecraft wiki entry for Woodland_Mansion, associated text: A woodland mansion sometimes generate secret rooms on each floor. A secret room can be one of the following type: "X" room, spider room, fake end portal room, obsidian room, birch pillar room, clean chest room, lava room, and attic room, with the 'X" room being the most common, and the "lava" room being the rarest. A way to look for a secret room is looking for gaps between normal rooms, this way is the best on the first floor, as there are no windows. Another way is looking through the windows through the second and third floors of the mansion, since some secret rooms are exposed to windows. A last way to look for a secret room is cutting down the roof, which works best for the third floor alone. Then you can see any secret rooms from the roof of the floor, as the whole floor's layout.