The Halls of Hunger

From the introduction:

Through millennia of effort and a thousand feet of living rock, the myriad builders of Dragon’s Delve finally reached the resting place of Iamon. Here, at last, those who have braved the Delve’s dangers can look upon the desiccated remains of a dead god. This is, of course, what drove the Delve’s construction, but it did not complete it. For, in the centuries since Iamon’s unearthing, Metterak has also imprisoned the moon goddess Glarias here, and built a formidable defense of his realm beneath this level.