Publication:Descent into the Depths of the Earth
PCs seek the home of the drow by traveling through an underground world of caves and passages. In the tunnels, the adventurers first fight a tough drow patrol, and the next major fight is with a raiding party of mind flayers and wererats, who have halted their patrol long enough to torture their drow prisoner. The characters also find a grand cavern containing drow soldiers, purple worms, a lich, a clutch of undead, a giant slug, sphinxes, trolls, bugbears, troglodytes, wyverns, and fungi.
The original modules Descent Into the Depths of the Earth and Shrine of the Kuo-Toa were both written by Gary Gygax and published by TSR, Inc. in 1978. Gygax had recently finished the Player's Handbook (1978), and according to Gygax, he authored the D series "as sort of a relaxation to get away from writing rules". Descent Into the Depths of the Earth, the first module of the D-series, was printed as a sixteen-page booklet.