You reach into your bag and pull out your notebook and write, "Help! Trapped inside!"

You slide the note under the door.

A few moments later, a note slides back under the door. You pull it out and read it. Your heart sinks.

It's just your note returned to you.

Another slip of paper appears at the door. You pull it out and attached to it is a length of string that reaches further under the door. You pull the string until...

The door clicks open. The string was attached to the handle on the other side. No one is there. The other side is still pure darkness. You feel like you have no choice but to try to leave now.

You walk out.

You realise your mistake. The darkness shrouded the floor, or lack of floor. You fall.

You fall forever.