Be awesome if it ended up being a randomised world underground too. Randomly generated while exploring it as big as the overworld without fast travel, populated with powerful (respawning daily) demons. Random useful items (food, weapons, armor, clean water) placed to give an adventurer a chance of survival yet still making it incredibly difficult. Map gets saved so a later adventurer encounters the same areas if already visited.
Maybe even impossible to access in dwarf mode(whithout sending an army there) So it gives more meat to adventure mode, by allowing a player to see how long they can keep their multi-legendary super adventurer alive in the depths of hell. Or a poorly equipped adventurer gets running in to try to get some easy gear only to become lost fleeing from the spirits of fire that just happened to be placed by the bottom of the stairs.
Of course it would need some kind of access point...maybe a spiral stair going around in a circle into a glowing pit. Maybe spawns a demon or 10 a couple times a year. I can imagine some players seeking that out just to embark on top of it and create a suitably evil looking castle. Even if they can't access the underworld in the mode.
Nothing to see here you people who donno bout HFS. Go throw a cat off a tower.
That gives me an awesome idea! And like all awesome ideas, it is shamelessly stolen from one of the greatest games of all time
Say there's this demon-world you mention, and everybody believes in it and has some vague idea about what it's like, but no concrete info.
Now, on a completely unrelated note, say that somebody (undoubtedly a dwarf) figures out a way to transport objects between two points almost instantly. It works perfectly with rocks and elf corpses. However, when they try it with surplus soapers brave volunteers, most come out the other end as a gooey red paste, and those who don't are little better than gibbering morons.
And then, one of the research forts is overrun by demons while the fort at the other end of the rapid-transit experiment vanishes. No bodies, no strewn equipment, not even the fort's tunnels: just a big, empty hole in the mountain.
So the researchers' race sends in an army, which is promptly slaughtered.
At that point, the demons are pretty much running rampant in a gradually-expanding area surrounding the non-vanished research fort. If you go there with an adventurer or dwarf-mode army, you find out that the rapid-transport system worked by sending the transported objects through the big HFS. Needless to say, the demons figured out how to use this system to get out of their HFS-world and into the mortal realm.
