1.Dig a 2x3 hole where you want your door to be. Place redstone in this hole.
2.Dig a hole that is 2 blocks long and 2 blocks high off the middle of the redstone. Dont dig the next bottom block but dig the top.
3.Place pistons where shown above.
4.Break the block to the left of the top piston. Place redstone on this block. Repeat with the other side except to the right of the top piston.
5. Add redstone to the 2x2 hole on either side. Place a redstone torch on the other block.
6.Fill in blocks underneath pistons. Place pressure plates on either side of the door for access. For further decoration place blocks on either side of the pistons to cover the redstone.