Tom Hall, and the other members of DIP (Developers of Incredible Power) started ROTT as an extension/addon to Wolfenstein 3D. The engine is an enhanced version of the Wolfenstein 3D engine. That said, let it be known that there were so many enhancements and added features that the final ROTT engine was basically its own engine.
The panoramic sky allowed you to take the player into outside areas. Bullet holes and breakable glass walls was a totally cool addition to the feature set. But more than that was the enhanced look of the game, upgraded movement, and a multitude of new dynamic effects to add movement and control for the level designer. And design Gorebagg did.
During the months that followed the discovery of the editor for ROTT levels Gorebagg made hundreds of small maps that were later refined into a set of more than a dozen full games. Again these maps were released to a lucky circle of friends. The mechanisms for public release of mods and levels was a little hazy at the time. So the immediate circle of friends, and friends of those friends lucked out.
The levels Gorebagg made were fun gaming. But, they were more than that. It was possible for Gorebagg to use the resource set to create many scenes and scenarios reminescent of Bardo spaces. This is, after all, part of the master plan for world domination: remind individuals of their prior experience in the Bardos, provide a training ground to become further familiar with the Bardos, and gain the experience necessary to effectively navigate the Bardos.
What the individual does with the added functionality is up to their attitude, aptitude, capacity, and orientation. Not much of a plan for actual world domination. But, he was on a roll so we didn't mention it.