Minecraft 3×3 piston doorway

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What is the most compact and simple way of making in Minecraft a 3×3 piston door?

Best Answer

The most compact way to make a 3x3 piston door is to make the door out of slime blocks, and have 3 sequential pistons pushing it up and pulling it down. This is achievable in a 3x3 area above, below or to one side of the door (excluding the door frame). There are many tutorials for these kinds of doors. Example.