I've recently started delving into Frog God Games Tome of Adventure Design and I'm experimenting with the location generator. The Tome is a fantastic resource either as a series of random generators or a detailed list of plot types, adventure ideas, potential monsters, items or simply a list of useful descriptions.
The location generator gives me a bit of a Small World flashback so the creation of adventure seeds from the Tome seems a bit tongue in cheek and if I had any skill at humor I'd use it here.
Adventure (Seed) - The Dream Barracks of the Brain Assassins
The Mind Flayer culture is dark and mysterious. Their language is strange and unoerthly, their society seems fragmented as they are found frequently in enclaves or individually among other societies but with no cities or nation of their own.
One legend says that they came down from Luna ages ago and their true home is there. Other speak of other planes or the Outer Void where terrible creatures of evil and madness dwell and that Mind Flayers are some combination of these beings with humanity.
Whatever the truth is Mind Flayers are a power within the Flanaess and the Brain Assassins are a power among the Mind Flayers.
Their leader, C'Reln, is said to be incredibly old and if his body dies he is reborn from a hidden chamber within a fortress called the "Dream barracks" whose location is known only to the leaders of the Brain Assassins.
The Brain Assassins operate mainly among other Mind Flayer's and Drow whose society is most openly populated by the creatures. There is a guildhouse of sorts in the major Drow cities, Erelhei-Cinlu, Urlisindatu, and other less known enclaves. A secret guildhouse is rumored to be in Rel Astra, Highport and even the City of Greyhawk.
The "Dream Barracks" is in actuality a place within the mind of each Mind Flayer. These creatures have something of a shared consciousness but it requires the use of a powerful magic item to activate among them. Those who belong to the Brain Assassins bear upon them a fragment of such an item allowing them to share consciousness with each other within a certain radius, said to be mere yards by some, but evidence points to perhaps a mile.