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.
How?
The wizard digs a 50 ft tunnel at 45 degrees downwards and piles up the soil he digs out below the window. The pile of soil allows him to reach the window and escape.