I see a lot of negativity directed toward adventure modules for a variety of reasons (from not liking the structure to not feeling they are necessary when you can make up your own material for free). My attitude toward modules has always been quite positive. I find modules helpful for inspiring me as a GM, useful for the spare parts they generate, and occasionally fun to run beginning to end. I have quite a few of them on my shelf, some I've run, some I haven't. All I have read and taken bits and pieces from.
Today I just want to focus on cannibalizing modules for spare parts. For me this approach is the most functional and rewarding. It also allows me to enjoy modules I might otherwise have little to no use for. If I can pull multiple NPCs, locations, adventure threads, etc from a single module over the years, then for me it has value.
Even if you don't like modules from beginning to end, they are great sources of spare parts to fit into an adventure and campaign. While I think a lot of people understand this, I have seen people express surprise that a module might be used for anything other than running it straight through. For those who have only run modules as written, or who have written off modules entirely because they don't want to run them from start to finish, consider viewing them as a source for spare parts. I recently incorporated a portion of Feast of Goblyns into my Swords of the North campaign (talked about it HERE). I hadn't used Feast of Goblyns in ages, but I am always pulling it off the shelf to get ideas or see if something from it will fit what is going on in the campaign.
Because I wanted to add in some horror in the Party's latest adventure, and because I knew I needed a cool lair for the blood cultists who are trying to thwart the PCs, the Cavern of the Undead Priestess portion of Feast of Goblyns seemed like a nice fit. To make it work though I had to change a few things so it would gel with the setting and with had had been going on in the campaign.
First I removed the undead priestess herself, replacing her with Abu Nutesh, a leader of the inquisition and a member of the Blood Cult. I decided to keep a lot of the undead priestess's minions, simply using their closest equivalents in the Sertorius rulebook. Because we already have zombies and other undead, this was mostly easy. Though I did have to modify some existing monsters in a couple of cases.
Second I took out the map of the Cavern of the Undead Priestess, re-read the description for each entry, then started writing my own to fit the needs of the blood cult, incorporating what seemed to work from the module itself. Some of the things I kept were the black mists that steal magic items (this was a kind of magical security system that could bring magical objects possessed by the party to Nutesh's chambers so he could use them), the giant skeletal sentinels around the parameter of the canyon, the canyon itself, the colossal skeleton tower inside the chasm, etc. I also reskinned a few of these things as well. For instance, while I kept the Skeleton Sentinels, I turned many of them into Giant Yaumbies, monsters in Sertorius that are like zombies by splinter into copies when wounded. There was also a quick wood tree in the canyon in the original module that served as a spy for the priestess. Because Sertorius has no quick wood trees, I changed it into a sculpture made to look like a tree and enchanted with Pora's Portrait. This enabled it to serve the spy function, but made it much less of a threat to the party.
The Cavern I used is actually just one area of exploration from the canyon described in the original module. I pretty much used a half of a chapter and a half of the book. But that was all I needed. In the past I have used other sections for different reasons (mostly when I have run Ravenloft games). This time was different because I was using it in a non-Ravenloft game.