A hollow world is not a new idea, and certainly wasn't one at the time the setting was made (just in case some of you young-uns reading didn't know that), but it was fun to see it integrated into the setting. Now, I'm not sure if the Immortal Ka's Spell of Preservation will still be in place as stated in the books, but just look at some of the key cultures contained therein:
- the Milennian Empire (think Ancient Rome)
- the Nithian Empire (think Ancient Egypt)
- the Azcan Empire (think Ancient Aztecs)
Even if we do go ahead and use these cultures in a different version of the the Hollow World setting, what purpose would they serve?
The Milennian Empire would allow some compare and contrast between the pre-Christian Roman culture and the Christian-dominant Roman culture.
The Nithian and Azcan Empires might allow me to rip off some of the 'Ancient Astronaut' theories, with Immortal-granted technologies used to create their grand pieces of architecture.
Unlike the current version of the Hollow World, however, I'd actually hold that these fallen empires were the source of the 'post-apocalyptic tech' that many people seek after. And perhaps they still serve the gods they worshipped -- gods who have fallen from influence but are still powerful.
In fact, there could be an echo of the Titans cast into Tartarus by the new generation gods here.
At the same time, I do want some mysterious areas in the Hollow World, places never conquered by these three still-active empires, but coveted by their leaders and gods. Sources of power that were sealed away for unknown purposes, guarded by beings and traps that can stagger even the Immortals of the surface world.
Usage of Hollow World
Another attraction is having creatures that are extinct (or thought to be so) exist in abundance in this world. Dinosaurs and giants of mythical proportions may walk here, as may some cherry-picked denizens of the Faerunian Underdark.
And what of Blackmoor? Well, Blackmoor would be my prototypical ancient astronaut / alien god city, complete with space ship and twisted technomagic devices.
For some completely off-the-wall ideas, one of the 'spell of preservation' effects could be an unpredictable resurrection / reincarnation spell that prevents people from truly dying. Unfortunately, it only works in the Hollow World. Once outside, you tend to die normally from old age.
As such, it can work as the Tartarus of myth where beings cursed by the gods live on imprisoned or tortured.
Likewise, imprisoned Immortals and gods would constantly be seeking escape if not for the Hecatonchires -- okay, I'll stop for now.
Hollow Worlds can be addictive.