Doom E1M1 map v1.1

Now, THAT is truly a blast from the past ... if someone had told me back in early 90s that I would be playing Doom level within other game itself, I would have called (and considered) them completely nuts!

By the way, for you Doom guys - there is something very similar to this, made for GMod, Source Engine. Basically a whole sub-system which brings & emulates Doom environment, sounds, weapons, even enemies themselves but within Half-Life 2. Kinda like the movie set, where the Doom level is spawned within other world (level), giving you dozens if not hundreds of combinations to try out. You can even combine Doom resources with Portal ones, essentially causing a mish mash of characters, maps & props. For example, Portal Turret & Half-Life 2 rebels fighting against Cacodemons & Imps.