this is a classic hidden door in minecraft, and it's a great way to hide all your stuff from other players. I am going to show you how to make it! :)
Step 1: Step 1: Make Your Wall
make a wall that's about 4*4 blocks high wall so you can hide your redstone stuff.
Step 2: Step 2: Piston
put some pistons in the wall.
Step 3: Step 3: Redstone
put the blocks that's the same to the wall in the pistons. and do the redstone like what I did on the photo.
right click on the repeater for one time.
Step 4: Step 4: On/off Switch
hide your switch and you are done!!!!!