Yes, it's from When Dungeons Arise. This structure is apparently called Keep Kayra. I don't have a problem with giant elaborate structures, even if this specific one I do think is ludicrously gigantic compared to the other ones. After all, I downloaded the mod myself and had an idea of what I was getting into. What I do have a problem with is that these buildings tend to repeat way too often. While I was mapping out the corner of the continent I started on I ran into several copies of the same exact structures multiple times, and since there is no randomisation when it comes to layout with these, they will always be the exact same structures which takes the fun out of exploring them.
Way south of this enormous tower I found a cool Arabian Nights-themed fantasy palace complex in a desert. It looked great! But literally right next to it was a copy of the same palace rotated 90 degrees which kind of took the impact away