24 May 2023

d12 Settlements of the Undercoast

Sparking off Creatures of the Netherworld from Studio Agate with their take on the duergar and their subsea cities - glass domes supported by their "sciencraft" - I got to thinking about the coast beneath the surface, the interface between the deep seas and oceans and the underdark. In our fantasy realms we have lots more dwellers below both on land and at sea - so how do their realms interface and where do they interact?

We have looked at our stacked up oceanic realms previously in d20 Aquatic powers and dwellers of the deep - the sunlight (1/8 mile deep), twilight (5/8 mile deep) and midnight zones (deeper than 5/8 mile). For a quick survey of the Underdark, we turn to Forgotten Realms Underdark from 3.5e, where we have the Upperdark (0-3 miles depth), Middledark (3-10 miles depth) and Lowerdark (from 10 miles deep to "unfathomable depths").

From this pretty much all our ocean depths are interacting with the Upperdark, which fits - this is the realm where interactions with the surface world are doable. The Middledark is a place of the deep adapted and wherever it might connect to the sea will be contacting the freezing 'abyssal' zone below even the midnight zone.

The Lowerdark is deeper than the deepest depths of the oceans, it runs deeper than the Marianas trench of our world. The seas of the Lowerdark are *the* deepest bodies of water anywhere. We have the Glimmersea deep beneath the Sea of Fallen Stars on Toril as an example. Setting aside the Lowerdark for now, we want to consider the open bodies of water and where they connect to the Upper and Middledark.

Below some underdark-deep ocean interfaces that can serve as ports of call on your voyage through the deeps or access either way. Unless mentioned otherwise, these are water-filled caves connecting to the ocean.

1. Sunken realms - cataclysms of various sorts, both the sliding of once surface realms beneath the wave and the flooding of underdark cities by the ocean can create these drowned realms; often initially rich in salvage, the pickings today will depend on who moved in afterwards and how organised they were. If a new city sprang up to replace this drowned one, often short-hop trade relations exist.

2. Underdark-ports for surface cities - in those rare places where surface geography denies a city a good port but decent access to the open ocean can be found beneath, ports spring up below with the underdark dwellers using this to their trade advantage. In some cases the trade caravans are wholly aquatic, in others they travel only as far as the coast before surfacing to transfer to ships - in either case the ease of water transport over land puts coin in the deep dwellers purse.

3. Tradegates - here subsea caverns, natural airlocks or ones created through artifice or magic, allow a lucrative trade between aquatic traders and underdark dweller holds. The underdark dwellers have difficulty venturing out to defend their approaches so these places tend to be fought over by aquatic factions with tolls for access exacted by the victors

4. Venturer ports - typically dwarfholds with massive airlocks from whence they might venture out to harvest the rich metals of volcanic vents or follow a rich seam out into the depths. The technical and arcane capabilities of the dwarves will define how exactly they are surviving beneath the seas but typically not so deep and with a very "boots on the sea-floor" approach, keeping the ocean off with a specialist helm and otherwise acting like it is just another cave.

5. Middledark miners - harvesters of metal rich nodules at the bottom of the ocean, different from the venturer ports in that they are typically burrowing *up* to get to the ocean bottom and are well below the survivable limit for all but the strongest magics there. Constructs, undead or aquatic workers operate out in the depths and bring back the wealth of the ocean floor to the massive underfortresses built to face off the ocean itself. Often communities of deep ocean creatures form around these things simply as they are a source of light and heat in the freezing dark abyssal depths.

6. Border forts - for cross-region realms (e.g. aboleth, mindflayer, kuo-toa) these are guardposts on the bounds of their realms, rarely a place to approach or interact with, more often the core of a zone of domination enforced to keep others away. Sometimes used as launch points for raids into other aquatic realms or the surface coast. Their dual-realm nature means they are extremely hard to siege. Active ones often have bizarre eldritch defenses - floating monoliths, time-space labyrinths, sentinel reefs, barnacle-encrusted constructs - enforcing a near scorched-earth zone around the fortress. Even abandoned these can be terrifyingly hazardous.

7. Raider camps - shallow, like pirate ports on access ways where sahuagin, kuo-toa or others raid the underdark for worked goods or underdarkers venture out for fishing. These are places that ask no questions about those who pass through, just provide them places to fence their takings and squander their loot on what pleasures they may want. Often some of the broadest mixes of folk can be found here and all sorts of bolt-holes and hidden stashes are peppered through the surroundings.

8. Temples or sacred grounds - for deities with domains across both underdark and deep sea - Blibdoolpoolp of the Kuo-Toa, the Demonlord Dagon - and can be interesting as a place where otherwise un-associated groups interact and can support actions in both realms. Depending on the deity and nature of the location, these can vary from unoccupied shrine to a bustling temple complex.

9. Faction holds - very rare as the expense of creation is rarely worth the gains - where similar to temple holds, coin drives some group to set up a place where disparate factions and groups can interact between the two realms. Often factions piggy-back on some other type of settlement so these only exist where no other reason if found and so are typically a costly endeavour to create and support. These are often complicated, highly magic-dependent structures designed to support outsiders in a very hostile environment.

10. Watchkeeps - outer defenses for some underdark realm, to keep sea raiders away - rarely the other way around to bottle-in underdark powers. These are places where no transit is desired, serving as a stopper through force of arms where for whatever reason a physical barrier cannot be created. Like border forts but even more hostile to those who approach from the wrong side.

11. Caravanserai - places for traders to rest, potentially places where beasts of burdens can be changed. different from tradegates in they are not a destination themselves, only facilitators of traffic. Caravanserai form when there are broadly equivalent power and wealth levels on either side of it - otherwise raider camps form. These can also be melting pots of different folk though often with less permanent residents as less wealth is spent by traders passing through.

12. Nomads gathering grounds - migratory assemblies - particularly for those where there may be underdark and open seas groups of the same peoples such as kuo-toa. Often seasonal, being thriving communities during the right circumstances then abandoned when the gatherings cease. Either high energy festivals crossed with grand markets or spooky abandoned site, figuring out which you want and when to find it is key for these.

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