From Ashes of Creation Wiki
- Expansive Underground Areas
- Some tight caverns but also much larger open areas, kind of a hollow earth but not literally.
- There will be a sizable Z-Axis especially where metropolises will grow, there will be room for the leader of a metropolis to fly a dragon around.
- Underrealm Node Development
- Underrealm Fauna and Flora make up their own ecosystem, not just a small tunnel 
- Seasons Underground
- Seasons above ground will affect what happens underneath
- Not a direct 1:1 correlation but you will see the effects from above happen down below i.e. tunnels might be flooded
- Won't see it snowing/raining underground
- There will be holes in the ceilings of some caverns in the underrealm that players will be able to fall/jump into from above. 
The Underrealm is the home of the Tulnar , who sought refuge in the Underrealm during the great calamity and atrocities that were taking place on the surface when the races of Vera fled to other worlds. [5:51]  [15:30] 
- Though still a very dangerous place, the Tulnar fled to the Underrealm as 'the last safe place' on Verra at the time of the calamity.
- The Underrealm is a rich environment where bio-luminescence abounds in the fauna and flora that exist here. These deep caverns and underground valleys provide new destinations for civilization to develop. Bringing the node system into the depths of the world may awaken darker creatures than the surface. 
- The Underrealm will have a great affect throughout the game itself, a part of the open world. It will introduce some unique elements such as the type of monsters you see, the type of crops you can grow and houses you can have. 
- The 'Zone of Influence' (ZOI) of the Underrealm could be directly under a surface Node ZOI and the two will not effect each other as would two nodes on the surface right next to each other. The ZOI of the Underrealm is more like it is on a different plane.
- Color will distinguish between different parts of the underrealm and will be influenced by their above ground region counterparts. 
- Meant to feel like individual regions of the world, but underground 
- Underrealm Caravan
- Underrealm Dragon
- Falling into Underrealm
|The World||Nodes • Castles • Housing • Freeholds • Underrealm|
|Nodes||Types||Divine • Economic • Military • Scientific|
|Stages||Expedition • Encampment • Village • Town • City • Metropolis|