A man is trapped in a dungeon in a castle in a far-away land.
There are only two doors in the dungeon; no windows or secret entrances and nothing to dig out through the foot-thick stone walls.
The first door leads to a room that contains a door out, but it also contains a fire-breathing dragon that will gobble him up when he opens the door.
The second door leads to a hallway of magnifying glass that magnify the sun's powerful rays and burn him to a crisp if he sets foot in there.
He has no weapons to defeat the dragon and nothing to protect him from the sun. How does he get out?