Midway through the Hebeth mission in Doom: The Dark Ages, you'll find a door blocked by fire shooting out of some broken pipes. Curious treasure hunters will want to know what's inside, but it's easy to overlook when you're racing from one fight to the next—this is one problem you can't solve with a meaty punch or shotgun.
The solution to this Doom: The Dark Ages Hebeth secret is hiding in plain sight, but to save you from sweeping the whole area multiple times like I did, here's what you need to do to turn off the fire blocking the door.
