There are a few ways to make trapdoors, but out of all of them, this one is my favorite. It's fast, completely hidden, and both opens and closes. This particular trapdoor can be used for a variety of purposes, such as hiding your valuable possessions, having a secret entrance to an underground lair, or maybe even taking care of obnoxious cows. What you'll need to make it are 12 sticky pistons, 8 redstone repeaters, 32 redstone, the switch of your choice, and whatever blocks you want to use to hide it. This is what it looks like when finished:
Step 1 Make a Hole
The hole needs to be a minimum of 8 blocks wide, 10 blocks long, and 3 blocks deep, as such:
It can be much, much bigger, or part of an existing structure if you want, but this is the minimum size.
Step 2 Make a Tiny Hole in the Middle
In the very middle, make a hole 2 blocks wide and 2 blocks long. It can be any depth you so desire, including all the way down to the bedrock!
Step 3 Add Sticky Pistons
Add four sticky pistons, facing inward, one block away from the hole. Do this on the sides where there are four blocks to the wall, not three.
If done correctly, there should be two empty spaces between your pistons and the wall. Also, note the cow in the background photobombing me. This cow is optional in your own designs.
Step 4 Fill in Blocks Behind Your Pistons
Fill blocks between your pistons and the wall to only one-block in height. That should be four blocks per side.
Again, cow optional.
Step 5 Place Blocks Directly Next to the Hole
Now you'll be adding two blocks on each un-pistoned side directly next to the hole, as such:
This cow was seriously freaking out about how cool this is. I don't blame him.
Step 6 Add More Pistons!
Now add two pistons (on each side, four total), facing up, between your already-placed pistons and the hole, as such:
And the cow decided to moon me. What a jerk!
Step 7 Place Your Repeaters and Fill In the Pistons
Your pistons now have an L-shape, and you're going to go ahead and fill that in with whatever blocks you want to show on the surface. In this case, I used simple stone, but you can use whatever blocks you want. Once you've done that, add two repeaters on each side behind your pistons, and set them on the third delay setting.
Hmmm, where did that cow get off to?
Step 8 More Repeaters!
Now you'll add two more repeaters to each non-pistoned side, with no delay at all.
Step 9 Wire It All Up!
Now all that's left to make this rig functional is to wire redstone around the bottom edge of your workspace, connecting all of the repeaters, as such:
Oh, that dumb cow got right into my trap! He deserves it for shaking his butt in my face earlier.
Step 10 Add a Power Source
At this point in a build, I like to just test the redstone to make sure it's working properly. Since the circuit is looped, you can add your power source anywhere you'd like and it will still work properly.
Works like a charm!
Step 11 Wiring
Now that you have a functioning mechanism, all that's left is putting the switch where you want it. If you want the mechanism to be ENTIRELY invisible with no redstone showing whatsoever, put a block at your place of choice in the redstone circuit, and raise the connection one block, as such:
Then just add another block above that, and put a switch on it. Voilà! No other redstone necessary, and if you fill the area in with a surface layer, it will be totally invisible.
Step 12 Filling It In
Activate the mechanism, which should raise the blocks to ground level, and then just fill in around them:
You now have a fully-functioning, hidden trap door! Once you've done this, don't forget to pop inside really quick and fill in these empty areas. They won't affect functionality in any way, but it's not very stylish to have your redstone showing.
Also, the cow was still stuck in that hole. What in the world am I going to do about this guy?
Step 13 Alternative Wiring
Say that you don't want your lever that controls the trapdoor to be on the floor. Maybe you want it on the wall instead. Well, all that you have to do is add some torches as I've done in the pictures, some more redstone, and then you're all set!
You want a redstone torch attached to the side of your block at the bottom that your redstone goes over, and then add another block directly above that torch, but with an empty space between them. Then put a torch on that block, and run the wiring from it.
The only downfall of this is that the top torch needs to be visible, as well as the redstone on the surface. However, those are easy to hide in a wall or to put out of sight in some other fashion.
Step 14 Deal with the Cow
Like I said in the beginning, the inclusion of a cow is totally optional. However, if you've chosen to take the cow route, you may find that you have a situation like this:
I recommend dealing with it like this:
Muahahahahaha! Cow annihilated!
Now tell your friends, "Okay, stand riiiiiiight there for a second, while I flip this switch...".