A big RPG module is an odd beast. The best analogy I can come up with is that they're like themed cookbooks. So a given cookbook might tell you how to cook, say, twenty different traditional Russian meals, and you could just cook them one after another in exactly the way the book tells you to, and that would be your dinners taken care of for the next twenty days. But you could also just cook half of them. Or you could mix them up, and pair the starter from one with the main from another and the side-dish from a third. Or you could have three or four different cookbooks which you dip into more-or-less at random. Or you could come up with your own recipes loosely inspired by the ones in the book. In fact, the 'cook everything in the book in exactly the way the book tells you to' approach is probably the least common way of using a cookbook, and the same is almost certainly true of RPG modules. I don't think I've ever run a module, especially a big module, in precisely the way it was written. Has anyone?
Liberation of the Demon Slayer is a huge six-and-a-half-level science-fantasy dungeon by Venger Satanis, containing something like a hundred and fifty rooms stuffed with Cthulhu cultists and naked slave girls and all the other things that Venger loves so much. I'm not sure that it's actually possible to run it by-the-book, because the module-as-written leaves out some essential information (like how the levels connect to each other), but if you tried it would probably take you months and months. I stripped it down to a one-level, twenty-five-room affair and ran it over the course of three-and-a-bit sessions. Every room was inspired by something in the original module, but not a single encounter was run in the way Venger wrote it. (I cut out all the random naked women, for a start.) Still, I'd like to think that the resulting game bore at least a film-of-the-book resemblance to the original module: it still had evil cultists and a crashed spaceship and collectable coloured trapezoids and a slug-blob monster and a fire shrine guarded by lava men and 0-level villagers looking for a magic sword. Had Venger been in the room at the time (or scrying on us like the freaky Cthulhu worshipper that he is), I'm sure he'd have recognised every encounter as clearly based on something from his book, even if nothing was left exactly the same.
Anyway, I ran it, and it was great. Ten zero-level peasants went in; seven first-level adventurers and three corpses came out. Cultists were beaten to death with frying pans. Poorly-thought-through plans were hatched to trip hobgoblins into pits of acidic slime. Spellbooks were stolen from druggy elves out of their heads on hallucinogenic fungus. A suspicious fat man was force-fed a poisoned mushroom on the grounds that he might have been a cannibal. One luckless PC set fire to his own legs in order to prevent himself from being swarmed by giant maggots. The final battle was won by waiting until the enemy were climbing up a steep slope and then dropping a raft on them. It was weird and random and funny and horrific and unpredictable, and I had a great time throughout.
How much of that was due to the module? Quite a lot, I'd say. I mean, yes, I completely rewrote the spaceship and the lava men and just about everything else, but it was Liberation of the Demon Slayer which gave me the idea to put them all there in the first place. It was the module which pushed me to work out why there was a crashed spaceship deep underground (and how it got there, and why it was now part of a dungeon with a magic sword hidden in it), prompting me to develop a whole science-fantasy mythology in the process. It inspired me to make things more weird and gross and silly than I normally tend to do. I might not have used most of what was in the book, but what I did use ended up carrying me a very long way.
If you want a huge dungeon you can play right out of the book, then you don't want Liberation of the Demon Slayer. (You probably want either Stonehell or Dwimmermount instead.) But if you want a big book of weird, vivid, and above all gameable ideas, so loosely connected to one another that they can easily be hacked into new shapes to fit your needs, you could do very much worse. It's full of pictures of naked women in peril, which are certainly not going to be to everyone's tastes, either in book form or at the gaming table; but I can attest to the fact that even after removing all the sexual material, there's still plenty of usable stuff left over.
Depending on what the players go from here, I might end up running The Islands of Purple-Haunted Putrescence next...