The PCs live in an underground shelter created by Voran Earthmane a long time ago. He made it as part of a series of chambers for his scientific research, along with a library and a keep, both of which have secure portals into the underground shelter. There are ten rooms that are magically maintained, a common room with a magically supplied store of food and ale, and an arcane laboratory, filled with instruments for creating and analyzing magic items.
The PCs found it when they fought their way into the library, located behind a cave. A group of kobolds was working under a dragonborn trying to excavate the library. The PCs killed the dragonborn and freed the kobolds, allowing them to live in the cave and library. Their leader, Bubbles, reports directly to the PCs, and is building his tribe up in their name.