I don’t know much about D1: Descent Into the Depths of the Earth because I’ve never read or played it (I can’t very well beg my DM to run a module I’ve read, after all). I have flipped through it though and I suspect it continues the pursuit of the Drow encountered in G3: Hall of the Fire Giant King through the upper reaches of the Underdark, encountering a variety of monstrous inhabitants along the way. Just a guess.

Though I am not sure if the name Underdark was used for the first time in D1, or in later modules in the series (it might not be used until 1986, in Dungeoneer’s Survival Guide), but this is certainly its first appearance.

In many ways, the Underdark – essentially a massive, planet-spanning dungeon – is a natural culmination of concepts Gygax was playing with through the history of D&D to that point. How many times can a party of adventurers go into a hole in the ground before they start to wonder if all the holes are connected?

The notion of the Underdark, with its myriad of warring societies and benighted wonders, is an immensely popular one and one of D&D’s most enduring locales. Dozens of writers and designers would explore in the coming years).

Its success should be no surprise. The idea of delving into the earth to encounter marvels has a downright mythic status in human imagination – from kids digging holes, to China to Odysseus descending to the underworld, to Jules Verne charting a course to the center of the earth. Of course Dungeons & Dragons would eventually go there in a grand fashion.

A quick art note. There is no illustration credit in the module, but Dave Sutherland’s signature is on all the drawings except one – the bugbears I included here. They very much look like Dave Trampier’s work, no?