Looked like the altar was flashing up to the left there.
Shrine's up and to the right from Ghostgate. It's a bit of an invisible side path for some reason.
Ah, even better, turns out there's a poorly documented issue with Rigmor of Bruma interrupting Immersive Armors startup for some reason. Turn Rigmor off, let IA configure, and then turn Rigmor back on. Fantastic.
Also, Cheese of Ages review: Fantastic mod. Slightly creepy in a place or two with some truly cringe inducing dialogue, but fantastic even so.