Averoigne

Module X2 "Castle Amber (Château d'Ambreville)" came with a bibliography of the eleven Averoigne stories by Clark Ashton Smith:

The Enchantress of Sylaire in "The Abominations of Yondo"
The Colossus of Ylourgne, The Distinterment of Venus, and The Satyr in "Genius Loci and Other Tales"
The Beast of Averoigne and The Holiness of Azedarac in "Lost Worlds"
The Mandrakes in "Other Dimensions"
The End of the Story and A Rendezvous in Averoigne in "Out of Space & Time"
The Maker of Gargoyles and Mother of Toads in "Tales of Science and Sorcery"

Try as I might, I could locate none of these collections when I first ran "Castle Amber" in the mid-1980s, neither in libraries nor in second-hand bookstores.  Then, one day, I saw "A Rendezvous in Averoigne" in Bakka bookstore in Toronto.

Cover to "A Rendezvous in Averoigne" (1988) published by Arkham House, with jacket and interior illustrations by Jeffrey K Potter.

This collection included four of the Averoigne stories "The Holiness of Azédarac", "The Colossus of Ylourgne", "The End of the Story", and "A Rendezvous in Averoigne" along with tales of Atlantis, Hyperborea, Lost Worlds, and Zothique.  I was hooked.

Map of Averoigne, by Ron Hilger (source: The Eldritch Dark)

Smith's Averoigne was based upon the French region of Auvergne, as discussed in "The History of Averoigne?" by Glenn Rahman (originally published in Crypt of Cthulhu #26).  Enterprising DMs therefore have no shortage of material to flesh out a campaign.

"The Averoigne Chronicles" (2021) edited by Ronald S. Hilger, trade paperback version of the definitive collection of Smith's Averoigne material.

Smith's Averoigne stories are now easier to access.*  Options include The Eldritch Dark, "The Averoigne Archives" (2019; see this review), "The Averoigne Chronicles" (2021), or even digitized issues of the original pulp magazines, at archive.org.

*a faux Ballantine version is unauthorized

(For capsule reviews on each of the eleven stories, check out this post on "Black Gate: Adventures in Fantasy Literature".  For in-depth discussion, see the Averoigne episodes on "The Double Shadow: A Clark Ashton Smith podcast".)

"The Averoigne Legacy" (2019) edited by Edward Stasheff.  Cover design by Jervy Bonifacio chosen from among 71 entries.

Averoigne continues to inspire, with "The Averoigne Legacy" collection of tribute tales, and music including the concept album "The Beast of Averoigne" by Haunted Abbey Mythos, and "The Bard of Averoigne" by composer Peter Scartabello.