Ptolus: Monte Cook's City by the Spire (5e Compatible)

Ptolus isn’t just big. It also feels alive. It’s a place you can inhabit—a place with an atmosphere you feel.
Ptolus is a massive fantasy city setting. The 672-page book (which comes with hundreds of additional pages of handouts and extras) gives you an amazing amount of detail, but is carefully designed and laid out to make everything easy to digest, manage, and access.