Openworld(-ish) Doom maps exist and OP is asking for them, not for discussion about whether Doom is suited for open world maps or not.
I can't vouch for the quality, but here's a few links I've seen floating around in "open world" threads:
Doom Free-RoamDawn of RealityEuropeEternal Doom IIIPlanisphere 2 (mentioned above)
The IslandNote that many of these may murder your framerate due to aforementioned engine issues.
Honorable mentions to Lost Civilization, City of the Damned (and its sequel Apocalypse), and Ashes 2063 for giving a
feeling of open-world even if they're not quite actually fully open by definition. There's definitely others out there.
