"It truly is something. As soon as you travel through one of the cavern entrances, you're in a totally different world. The air is cooler in a lot of places and there's an overall dampness you can't quite escape. Both natural and man made tunnels are everywhere. It's not hard to get lost. At least a lot of the mushrooms provide some light." - Portion of a blog entry by Birki KroonOnly found on the main island of Omari, the Underdark is home to many subterranean species. It consists of winding tunnels, deep caverns, settlements carved into the rocky terrain, and even a couple lakes. More people have been allowed to visit and move in during the recent era, however, its primary population still consists of light sensitive species like the dark elves, deep gnomes, and cave dwarves.
A Dark Refuge
During the Era of Beginnings, the Oizai opened up their new islands that Uxali and the gods gifted them after their native island was lost to the sea. There were many other islands meeting the same fate as theirs. When they discovered that their largest island had a preformed underground system, they offered up the area to some of their newest residents. They took note of how uncomfortable some species were living in areas with little light protection. Some of the islands they left had little to no light during a majority of the year.
Being one of the first to the islands, the dark elves took the Oizai up on this offer and set out to make their new homes. Other species were soon to follow. They were very grateful for this kind offering. Before the Era of Strife, relations between the Underdark and the surface world were amicable and open. When tensions escalated between groups above them, the current queen of the time decided to seal off their entrances and forbid interactions for several centuries. It wasn't until the Prismatic Era that they would reopen, albeit with great hesitation, and resume relations with the surface world.
Underground / Subterranean