Here's a shot of the game map.
1 - Start Point - Grab the camera right in front of you and right click when the monster gets too close to banish it.
2 - Get the yellow key.
3 - Go in the Yellow Door Room and get the black key.
4 - Play the piano and get the blue key.
5 - Go in the Blue Door Room and use the switch.
6 - Exit the stairs (you can't exit before the switch for, uhm, reasons...).
After you exit, you will be chased by a monster, so run to the right as fast as you can! Hope this helps.