Termite mound

A mound of giant termites have built an enormous nest here, protecting their queen and tending to an underground fungal forest that is also home to some myconids.  It has built up around a ruined tower of a mage, and underneath a giant Chaos godling-beast not unlike an anteater lives here, feasting on the termites and acting as host to a small cult dedicated to his worship.

(Ideas happily stolen/adapted from here)