Materials: 6 Pistons, 4 Pressure plates, 2 Redstone torch's, 14 blocks,12 Redstone and 4 glass blocks
Alright let's get started.
Step 1: Pistons
Place 3 pistons on top of each other, then 4 blocks to the right, do the same. (make sure there facing inwards)
Step 2: The Hole
Dig a 2 block hole as shown in the the picture.
Step 3: Redstone
Place a block on either side on the middle of the 3 pistons and put a redstone torch under and redstone dust on top.
Step 4: Covering Up the Hole
Cover up your hole, then, place your pressure plates 2x2 on each side.
Step 5: Finishing It
Now put your glass blocks on the sticky pistons.
Step 6: Adding a Few Touches
In this step you just cover up anything that you want to.