In 1963- post test ban- a nuclear detonation under the Nevada desert knocked a hole in reality....And it just gets more awesome from there. Lots of great, short, in-setting accounts of hardcore special ops types venturing into a mindbending subterranean hell full of unspeakable horrors and all-too-tempting prizes. It works. It absolutely works. I would absolutely play a modern military dungeon dungeon crawl game that gets into the drastically weird scientific implications of its setting, and the impact its discover has on the world above.
The bomb was something new- and still classified- but what it did was stab through the fragile skein of normal spacetime the whole visible universe occupies, and opened a hole into something stranger.
The Fed put a door and a lock onto the hole- ninety tons of steel and titanium strong enough to bounce nukes. They kept it secret too. The place the hole opened into was just to weird for people to know about or deal with. It's variously called The Basement, Downstairs, and for those who hide behind terminology, the "Subterrestial Operational Theater".
In the late 70's, one of the young computer boffins working on the project called it "Gygaxland".
By the 90's, everyone was just calling it "The Dungeon" despite the term being officially verboten.
The name fits though. Under reality, in realms so strange they defy scientific models to explain, someone or some thing built tunnels, chambers, traps, lairs... but also filled it with wonders and treasures- including objects and devices which could quite simply, do the impossible.
Project: LONG STAIR was born.
Of course, last thing I've got time for now is another game, but it's nice to keep stuff like this in mind for the future.