I agree that this module is somewhere between an adventure and a gazetteer. You can run the adventure and still have a huge amount of extra setting information that allows you to run a sanbox or create a number of other linear adventures in the very same location.
Some descriptions are at times even eccessive ;)

Added Drivethru link to the OP.

-Havard

This is a super classic module by Dave Arneson (nonetheless) and it is in the history of roleplaying, but it is also a high demanding adventure for both the players and the game master, as there are many details that need to be presented, noticed and properly processed. My impression, after running it twice on RPoL (with plenty of difficulties), is that it isn't really suited for play by post, as the times of play by post are too long to keep in mind and connect all the dots. Of course this may be just my problem, all due to my being a bad GM.

This cover art is absolutely iconic and speaks volumes.