From the release:
The City of 10 Rings is a great metropolis of dark fantasy and eccentric NPCs. Within the pages are sections devoted to each of the 10 areas (or rings) of the city, that describe 100 pathways, 100 locations and 100 possible events that could occur when exploring - to give a Tale-Weaver inspiration for 1001 adventure-seeds.
The City of 10 Rings can be used as an idea-generator for whenever PCs encounter a large, mysterious city. It also introduces additional names and NPC's for use within the Nights of the Crusades setting.