The Mirror Cities of Gulthias

Publisher's blurb: Beneath the ancient Gulthias tree is buried an even older city of Elvish design, populated by strange inhabitants that seem to be slaves of the tree. After exploring the city, you’ve found that there are strange passageways buried through the roots in the middle of common pathways, leading to a mirror city underneath. This city is suspended from the roots as the city it mirrors above is built on top of the roots. A darkness falls over this city, and you step carefully from root to root lest you fall into the deeper darkness below.