The 12th module in the Dragonlance saga (although only the 10th playable one) focuses in and around the underwater city of Istar. A city destroyed in a world changing cataclysm which had curiously also been the theme of the recently released first volume in the Legend of Dragonlance series of novels: Time of the Twins.
It’s fun to see these synergies going on in the world of D&D releases and it’s only something you really get if you either lived through it or do this kind of chronological run through the releases. So, if your players were avid fans of the setting (and seeing as they’ve played through 10 modules of the series and probably read the massively popular Chronicles novels, they probably were) they would have been pretty well informed about how Istar came to be the underwater city in a sea of red that it is now.
The module is pretty long, with a lot of lore content as well as a more sandbox feel than some of the previous ones, as you get the Istar setting with plenty to do in it. The adventure also allows for use with the Battlesystem wargame for a massive underwater urban battle. Good stuff.
D&D History 
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