New type of sub-biome: subterranean

It would be great for us spelunkers and for realm diversity if a subterranean sub-biome could be added to the pro-gen realms.

Concept: For each biome (desert, forest, swamp) have variants that are primarily or entirely subterranean, going with the themes of those biomes.

POIs: In addition to the standard POIs re-designed specifically for the subterranean variants include cave-related POIs, such as:

• Mining outposts that need resources to repair their equipment (either essence reward or rare material reward, like platinum or other metals you can't mine yourself)

• Realmwalker camps with injured and other "in need" individuals (mutliple Aid missions in one camp, or one big one) who need medical supplies or other material support (essence reward and maybe lore that you would otherwise get from Hope Echoes to fill in missing gaps, or even special lore. Sharing information and all that)

• Clearance requests to kill all creatures in a cavern or tunnel, such as for an expedition that needs help to continue, or for one of the outposts that has come under attack from them (creature corpses disappear like Bound, with essence reward and appropriate tier hides/meats/bones)

• Special fabled hunt missions. For science. (creature materials harvested from fabled, essence reward from chests)

• Find a well-hidden fae sanctuary (hidden quest with no POI markers, and not revealed on the map until found. Essence, lore, and maybe some fae material rewards such as the metals and gems used to make automatons, or rare resource nodes. Similar to one of the forest biome caves, have a small opening in the rock that you can easily miss if you're not looking, with a small zig-zag to make it so you can't see the sanctuary unless you go in)

I'm sure others can come up with various ideas for POIs and missions.

Resources: Primarily ores, gems and rocks. Include lakes and streams for fishing (and to make it more exciting to explore), with the fish being the same as their source biome (desert, forest, swamp). Possibly add some holes in the ceiling that create oases of life where special trees or fibres can be harvested (like ebonwood and flax), unique to subterranean variants. Creature materials, standard and special.

Formation: Networks of tunnels connecting caverns of various sizes; some caverns as single-entry rooms, some tunnels as dead-ends. Vertical and horizontal layouts, including deep pits (common to a lot of cave systems), terraced caverns, vertical tunnels (some hidden) and sloped caverns/tunnels in addition to standard horizontal layouts. Lakes in some caverns. Rivers/streams that sometimes follow tunnels, sometimes go into the walls. Sometimes hide passages to other areas by a small gap of rock above a lake or river so you have to swim through. Stalactites/stalagmites used both as standard terrain (including for grappel travel) and as pillars for fae and/or human outposts.

Potential for expansion: In future updates, if they are added, includie variants for snow/ice biomes and fire/lava biomes, creating environments that make resistances more important. Special "safe" zones can be added such as realmwalker camps with fires for heating, or rings of fae glyphed stones creating a sanctuary.

Additional: The charm boosting subterranean damage would be less of a niche thing that would see more use (currently caves and bunkers are a tiny minority any realm, making them not very useful).

Conclusion: Adding a greater diversity of realms will add more excitement to player experience. Underground biome variants would add new dimensions to combat, exploration and travel, and bring out others that are severely underused. The standard proc-gen biomes are beautiful and great to explore, but I've always felt that real cave systems are sorely needed; rivers that delve through terrain creating tunnel systems and caverns in standard biomes would be a great addition to what exists, but why stop there?