There's also a handy bug in it:
Walk as close as possible to a wall, or a closed
door you want to go through. Turn back, start
running away and immediatly, turn back while
running, towards the wall. If you release the
[Shift] fast enough after starting to run, you
go thru the wall.
You will have to play around with that [Shift]
key a bit to get the hang of it.