Minecraft wiki entry for Secret_door, associated text: Almost identical to the hole in the wall, this is exactly what it sounds like. To create it, simply dig a hole in the ground, add ladders to allow upward movement, and build a base at the bottom. It may be tempting, but remember to not dig straight down. This door has the advantage of only taking up one block of space and being able to be built anywhere, not just places with walls.