An evil king locked a wizard in a dungeon with nothing but a chair and a shovel. There is a window in the room, but the wizard can't reach it using the chair. The dungeon is surrounded by a cement parking lot that stretches 100 feet in every direction.
The wizard uses the shovel to dig a 50 feet long tunnel and still manages to escape.
The wizard first collects the dirt which has accumulated from digging the tunnel until it is sufficient to make a pile to reach the window of his cell, and thereafter, he climbs out to his freedom.