Logic Puzzle: Step 3

Welcome to the land of the absurdly logical.

Here's your third step:

You are in a room with three doors. One door has a sign that says 'I am a door to the outside world'. Another door has a sign that says 'I am a door to the inside world'. The third door has no sign, but you know that the sign on one of the other doors is a lie.

What do you do?

Or, if you're a rebel, try the Rebel's Path