[jka]

It's a shame that (if I remember correctly from the video?) the bug that allows this is restricted to single-player; if not, I suppose it'd be possible to start the "outer" map as a network game, and then use the second instance of the game to join the outer instance over the network (including the possibility to walk around and find the original player character).

[e9]

Or create inception type game play in doom where you don’t know how many levels deep you are from original game lol