In Minecraft, hidden doors are a great way to keep your base or other areas secret from other players or mobs. They can be made using a variety of materials and techniques, and can be customized to blend in with the surrounding environment.
One of the most popular methods for creating a hidden door is to use a piston door. Piston doors are made using sticky pistons and blocks of your choice. When the piston is activated, it will push the blocks out of the way, creating an opening. When the piston is deactivated, the blocks will fall back into place, hiding the door.