Almost 25 years after it was released, Doom 2 has finally given up its last secret (with some qualification as to what the secret really is).
It’s secret No. 4 on Map 15 (Industrial Zone). Now, the area in question has been known, seen and accessed by other means (usually a noclip cheat code). Getting to it without a cheat appears to be deliberately impossible, according to Doom co-creator John Romero.
Romero tweeted out congratulations to the solution’s discoverer, Zero Master. Zero Master figured out that the way to trigger the secret was to be pushed into the secret area by an enemy (in this case, a Pain Elemental). Romero’s explanation shows that what has been considered a glitch was instead deliberate.
Secret explained: A secret teleporter is marked as a discoverable "secret", but when you touch it, you never enter the sector. So you would never get inside the teleporter sector to trigger the secret. The only way to trigger this secret is to be pushed by an enemy into it! #doom— (@romero) August 31, 2018
What this means is, Zero Master is the first player to get 100 percent secrets discovered on level 15, using the game as it was originally coded. (Later ports ended up fixing this “bug,” but the original MS-DOS version does not). As user mcc111 put it on r/speedrun, it also means that Zero Master “has the first legit Doom 2 100% save file on earth, after 24 years.”