I honestly wish someone had answered you after all this time, b/c I've got the same mod that causes the same altar to appear (assuming that you're speaking of an altar north of Solitude)... I also can not figure out what mod this goes to or how to open it. Not even console commands seem to work. I believe it's the topside for the quest from Lilith's Tools. I know this is a couple years late, but similar plight to yours, and I found myself in there...I think. Though not via that entrance, but an underwater one nearby. Course, now that I'm at the end of the dungeon, I can't... get... out.
