Create a hidden passage underneath stairs.

There are a lot of secret passages and entrances you can make in Minecraft using pistons, here I will tell you how to create a hidden entrance underneath a stairway. Like the image below.

Step 1: Place 2 sticky pistons next to each other, with one of them raised 1 block, like so.

 

Step 2: Wire them up as shown.

Step 3: Add a lever to the stone block and pull it so that the pistons extend.

 

Step 4: Build the stairs.

Step 5: Pull the lever, the stairs should move and you can now add steps going down into your secret passage.

 

Your hidden staircase passage is now complete! You can hide whatever you want down there.

Minecraft Pig:
Nobody will ever find my cake now!

You may also want to read:
How to build a hidden lava entrance