The Underworld calls! Can you resist its dark lure? Deep within the Underworld of 13th Age's Dragon Empire lie adventure and treasure-as well as madness and death. But what is reward without risk? The Book of the Underworld uncovers the secrets of this vast and mysterious realm, including:

* The lands of the Underworld: the Underland, the kingdoms of the Hollow Realms, and what lies within the Deeps

* The mighty dwarven city of Forge, rallying point for the inevitable war to reclaim Underhome

* The domains of the Silver Folk elves, and their underground icons: She Who Spins in Darkness, and He Who Weaves with Joy

* The threats of Malice, the Drowfort, and the four kingdoms of the Mechanical Sun

* Forgotten gods, the gnome academy of magic, monsters, magic treasure, and more!