Step #119 in the Expanded Vanilla list
From the Nexus description:
Caldera Mine Expanded is a mod that enhances the Caldera Mine area, making it seem as important and high-priority as quests and dialogue made it out to be. The vanilla location is dead, lifeless, and doesn't seem like one of the largest workplaces in all of Vvardenfell. Caldera Mine was impressive in vanilla Morrowind, but it didn't quite live up to the lore around it. This mod aims to fix that.