This is a rather strange supplement. It's not an adventure, yet it can feature in your games. It's a location and an individual, drawn from the world of Lankhmar, and in a way serves as an introduction to this wonderful place. If you want, for example, to move an existing campaign to Lankhmar you can have the party discover the entrance to the cave somewhere in the current campaign world...
The first part provides a description of both the cave and its owner, a wizard by the name of Ningauble of the Seven Eyes. If you know Lankhmar already you are probably familiar with him, if not suffice to say that he is a... well, it's a bit difficult to describe really. Somewhere within the caves squats something, something that appears man-like, cloaked, with all that you can see of his features being seven glowing eyes. He's one of the two most powerful sorcerers in Nehwon, opinions are varied as to whether he's the most powerful one. (He thinks he is, and it's probably best not to argue, certainly not if you are with him at the time!) Nobody knows just what he is, although rumours about. His passion is the gathering of information, rumours and facts are all grist to his mill.
Unlike most Nehwon wizards, Ningauble is not solitary by nature. He loves gossip, lore, stories and even the occasional fact far too much, and is always in search of new people to bring him such choice snippets... the party will soon fall under his sights if they have not done so already. Once someone has become one of his 'Gentles', as he calls his spies, he never lets go, although years may pass between assignments. One day another of his missives will turn up. Some seek him out, asking for his patronage in return for services, others he picks out as useful. They'll get the patronage, but he'll demand the services he wants, and is not above blackmail or threats when necessary.
Next, we find out about the cave itself. It's all a bit allegorical, but when you are actually there it is real, frightenly so at times. Somewhere in the middle is the Audience Cave, where Ningauble himself is to be found. There are other folk here as well. Other Gentles. Creatures which dwell here. Creatures which have just wandered in and not found the way out. These and more may be encountered (and, yes, there are random tables for when the party visits). The cave has many entrances, likely into several worlds and other places. One's Nehwon, of course, and one may be your campaign world... or indeed any other place you'd like to take your adventures.
There are plenty of examples - places you might emerge into and things that might happen in them, encounters and their consequences - to get you going. Indeed there's material here that could spawn a whole bunch of adventures, pick the ones you like and develop them into something that will keep the party coming back to the Caves for more.
Finally, Ningauble is written up as a full-blown Patron according to the Dungeon Crawl Classics RPG rules, should you decide to use him that way for one or more members of your party.
Overall, there's a lot here to delve into. Some won't make much sense out of the context of Lankhmar, but if you do know it everything hangs together to bring the rich strangeness of it all to life at your table.