Go to level 30, Icon Of Sin. Collect all the items,
then enable the iddqd code. Go through the warp, then enable
the idclip code. Go backwards until you get to the skull
switch. Blast the demon that appears with two rockets to kill
it. Activate the switch. Go on the rising platform using the idclip
code. Do not walk through the wall of the demon. Blast the demon's
forehead (the part that makes skull boxes). This will hit the
head on a stick inside. You should be able to hear a roar. The
rocket box on top of the platform can be collected an unlimited
number of times, unless you collected the box beforehand.
Strategy: by Aardvark