On most multiplayer servers, protecting your house is a must. One way to protect your house is to prevent people from even knowing where your house is. To accomplish this, one should use a hidden door. Ranging from a hole in the ground to an elaborate piston contraption, building a secret door can be as easy or as hard as you want it to be. Some hidden doors are more reliable than others, but it is up to you to decide which door to make. Extra security measures can be added to any of them, and several hidden doors can be combined, but most of these doors have some sort of drawback. This article will aim to cover the basics of a few types of hidden doors.
 Fishing in lava door
First off, you need a lava pool. This can be either natural or artificial. If you are, make it look natural. Put a WOODEN pressure plate somewhere at the bottom of the lava pool. Remember where it is. After this, you must dig under the lava pool, and put redstone wiring beneath the pressure plate, connecting it to a piston secret door. When you wish to enter your base, fish at the wood pressure plate. If the fishing bobber hits, the plate will activate a redstone current, opening the door. To close the door after entering, retract the bobber. A button can be used to get out. But then again, people will question why you're fishing in lava.
 Secret Painting Door
Start by making a 1x2 gap where you want your doorway to be. Be sure that the wall area around the secret doorway is big enough for the size of Painting you want. For example, for a 2x3 painting, you will need 2 blocks on both sides of the secret doorway, because the doorway counts as 2 blocks. The painting will not stay on the wall unless you follow the next directions carefully: First, place a solid block in the bottom of your doorway, and in the top section place a sign.
To put up the painting in the right spot, look at the lower left-hand corner block of where you want the painting and right-click on that block (hint: you may need to replace the painting a few times to get the right size).
A way to make the doorway easy to enter is by making a 2x2 hole and putting four signs on the side, then use the sides of the signs to put up a 2x2 painting, allowing a bigger hole to walk through.
There is a second method to this as well. Simply place a regular door into the wall, they can be single or double doors. Open them and then place a painting as you would regularly do. The doors register as full blocks, so the painting will go over the door seamlessly. The important part is having the doors be open, because there is no way to open them through the painting. The doors can be powered by redstone to form a solid wall upon first inspection, then open up to reveal a hidden room with the push of a lever, pressure plate, or button.
If you would like to make a higher security version of this door, it is basically like the above method. Instead of having a lever or button out in the open that anyone could find and open the door with, you can dig out a block next to the door but still behind the painting and place a wooden pressure plate in the opening. It MUST be wooden. Remember where the plate is and when you want to open the door, throw an item through the painting and onto the plate. The door will open, you will walk through the painting and door, and it will close behind you after you pick up the item on the pressure plate. It is good idea to use iron doors if you are near a village because villagers opening the door through the painting (which they can do) would give it away.
 Piston Hidden Door
For secret doors involving pistons, see the Piston Uses tutorial.
 Underwater Hidden Door
Doors and entrances can actually be hidden underwater. This is accomplished via the use of water blocking objects such as trapdoors, ladders, signs etc. Many players prefer to hide these underwater entrances in man-made fountains, bodies of water or behind/in waterfalls. When creating an entrance in the base of a body of water dig a small hole, 1 block only is hidden the best. Then place a ladder at the entrance of the hole, you should see that this will block out the water, leaving an air pocket. You can now continue this ladder shaft down into your base. Be careful when placing torches or light sources to not make this hole easily noticeable.
This secret door can be coupled with a piston and a wooden pressure plate to make your base hidden even better. The player tosses an item into a hole a short distance away from the door. This hole can either have the pressure plate in it, or can have a water stream to move the item, and be either above or below water. When the item lands on the pressure plate, a redstone signal retracts the piston, opening the door. After entering, the player can collect the dropped item to close the door. A button can be used to open the door for enough time to swim out.
 Lava Door
Minecarts can be used to teleport through lava, and your player will instantly be inside the minecart without actually having to go through the lava. This can be used to your advantage. First, make your doorway (at least 3 layers) of blocks as the door frame. Then place one minecart rail on the floor outside the doorway directly in front of it, and another inside, directly behind your doorway. On each of these rails, place a minecart. Optionally, half steps may be placed around the rails to keep the minecart from being pushed. Remove one block from the top middle layer of the door way, and remove one directly below this hole on the floor as well. Then get a bucket of lava, and place the lava into the top gap inside the doorway, being careful to move out of the way immediately to avoid getting a faceful of lava. You can now use your Lava Door by clicking through the lava to the minecart on the other side.
On the side of the doorway that is open to the rest of the world (aka the people you're trying to keep out), remove the previously mentioned half slabs and build a convincing minecart track off of where the minecart sits. this ensures people won't wonder why a random minecart is sitting next to a lava flow, as they will probably assume that it is a minecart incinerator rather than a secret entrance. one problem with this is that the minecart may be acidently pushed into the lava by another player while you are inside your base, thus trapping you inside. a way to fix this is to set up a redstone torch to turn on while a cart is sitting on a detector rail in front of the entrance so you know if it's safe to attempt teliporting through to the outside. to throw off even the smartest people who would question why you have a detector rail in front of your supposed minecart incinerator, you should also wire up the detector to a mechanism that looks important to the automation of the system, which, once again, is supposed to be a minecart incinerator. please note that it may be more convenient to build your secret entry way into an actual minecart incinerator than to build a fake minecart incinerator around your pre-existing secret entry way as this optional step describes.
 Lava and Water Entrance
This entrance is extremely dangerous, as the player is required to go into lava briefly. In addition, it is impossible to exit, unless the player uses a fire resistance potion. However, an inefficient exit may be formed by making a 1-way portal to a very high platform, and then jumping into water below the platform. Dig a 1*1*5 hole in the ground. Place a sign inside the hole, 1 block below the opening and 3 blocks above the bottom of the hole. Place another sign one block above the bottom of the hole. Fill the lower 1*1*1 gap fully with water, and fill the top with lava. The signs hold the water and lava in position. When you enter, you fall through the lava into water, then into a 1*1*2 hole. You can use this to continue building a passageway.
OPTIONAL: Build a 5*5 hut around it with a door, with a sign labeled "Trash Deposit" to fend against anyone thinking that there is a secret base in there. The lava will also trick them! You should also place a door in front of the lava so the lava doesn't flow out.
WARNING: Make sure to wear armor, or use a potion of fire resistance! If you do not, the lava will kill you and your inventory will fall in the lava!