Step I
Find a side of mountain.
Step II
Crouch and dig a Two x One hole until you reach the other side.
Step III
Go Two blocks back, then dig in Three in, on the Third block back on both sides, then dig out two more rows of three in behind the first row on both sides.
Step IV
Go to the front of your bunker on dig two in on each side so you have a Hallway that should look like this
_ _ _ _ _
_ _ _ _ _ 1 _ is 1 block
Step V
Then delete the blocks in this pattern.
| |= 1 Window where blocks used to be.
_ | | _ _ | | _
____________
Epologue
Go back to where you started the tunnel and block it with two blocks that are camouflaged.
Hope you enjoyed your Bunker, that only used two blocks!