Descend into the middle story, then make your way through the stairs in the middle. They appear to 
lead nowhere, but there is an invisible floor. Jump to hide the invisible wall in the middle of the
invisible floor blocking your way. Proceed up the second set of stairs leading to the exit. It 
appears blocked, but there is another invisible floor you can run on without the entity in the middle
of the room disintegrating the stairs. Use this to disintegrate the wall blocking your path to proceed
through the rest of the level, which is fairly straight-forward, utilizing all the skills you will 
have learned earlier in the game.