Take a very particular group of materials, place them on a flat surface and then apply a lighter and the resulting chemical reaction will somehow summon the most evil-looking thing in creation.
Nicknamed 'lucifer's squid' this experiment is actually two reactions taking place, the first being the decomposition of ammonium dichromate which results in the jet black volcano.
The second is the combustion of mercury (II) thiocyanate, which causes the enormous tentacles to appear from within the mound.
Short of CGI we'd argue this is the closest you're going to get to seeing the gates of hell. It looks harmless, incidentally, but you'll be hard-pressed to get hold of both of those chemicals at your local shop. So don't try it.