Underhollows

The surface of the dome of Aiaos is just a small part of the material realm. Sewers and catacombs, the streets of previous cities, and honeycombs of goblin brags and kobold warrens lie beneath every inhabited area. Dwarf and gnome communities occupy deep halls underneath the mountains. These subterranean areas are largely stable, as Aiaos is not seismically active, but there is always a risk of deep excavations breaking through into the Underhollows - or of something breaking out. Beneath the commonplace underground, the Underhollows are the deepest physical locations in the World, a sunless demimonde of tunnelling monsters and deep-dwelling kin to surface lineages. The distinction between underground and Underhollow is not hard and fast, but is determined by a mix of depth, occupation and ecosystem, influenced by a specific saturation of Dark Energies.   The Underhollows are the deep places beneath Aiaos and the domain of the Underfolk, those who live hidden from the light of the sun. While some of the burrowing fauna are quite unique, most of the intelligent underfolk have roots shared with the surface lineages. These include hollower Dwarfs and deep Gnomes, the Kindled and certain lineages of Seafolk, as well as many Kobolds and Goblins.   Many on the surface see the races of the Underhollows as degenerates in the service of Hell, and some among them of them no doubt are, but many of them serve as a bulwark against the Abyss, and the long-buried dominions of otherfolk that the surface has forgotten about. The kindled and thehollowers in particular have a long tradition of custodianship over things that ought to stay buried.  

Underhollow Spaces

Underfolk define areas of the Underhollows not by the stone that surrounds them, but by the space in between.   The bulk of the Underhollows is made up of the Caverns, the natural caves and tunnels. The Caverns are typically more open than regular underground caves, with many areas large enough to house entire cities between their floor and roof. Over time, many of the natural passages have been widened and paved, but are considered part of the Caverns so long as at least half of the space was there before any stone was cut away.   If a space is mostly artificial, it is part of the Tunnels or the Cuttings. The Cuttings are artificially-created residential spaces, a mix of vaults - large, open spaces - and combs - houses and halls dug into the stone. An occupied area of the Underhollows is part of the Caverns if structures are built in an existing or enlarged space, and part of the Cuttings if it was dug into what was previously stone or earth. Many settlements combine Cavern and cutting space, often using the stone dug out of the new Cuttings to create buildings in the Caverns.   The Tunnels are passages out between occupied areas, and are considered one of the most dangerous parts of the Underhollows. Because of the dense occupation in the Cuttings, tunnelling monsters tend to avoid them, but the Tunnels are treated as an intrusion into the territories of many Cavern dwellers and burrowing creatures, and travellers in the Tunnels risk being attacked by predators or bandits.   More dangerous, but much less travelled, the Darkenings are the areas of the Underhollows that are corrupted by necrotic, Abyssal or Void energies, and which provide a sanctuary for cultists and a spawning ground for undead, aberrations and friends.   In the deepest parts of the Underhollows, the Fathomless Vertex breaks through from The Abyss. This passage from the material to the Abyss is held by infernal forces, but contested by the demons of Alathkthi, corrupted drow servants of the Demon Prince known as Lilloth the Netweaver, colonies of Outerfolk and guardian clans of drow and duergar.