From publisher blurb:
Every Kingdom has to start somewhere!
The Kingdom Seeds series presents small settlements that can be dropped into a campaign as an early base or used in conjunction with the kingdom building rules to flavor the starting town or hex. This installment takes a trip to the Underground. Now with new sidebars that explore unique feats, magic items, equipment, alternate racial traits, variant monsters, and more.
Lawless, law-abiding, or unbothered, Kingdom Seeds: Underground has somewhere and something for everyone.