Step #107 in the Expanded Vanilla list
Be sure to also grab Balmora Underworld Nav Point Fix (list readers: it's next).
The author notes that some cells have quite a high object count, this might affect your game's FPS. This mod has also been noted to have problems with the Dwemer elevetors when
OPENMW_PHYSICS_FPS is set to 15.
FLG - Balmora's Underworld V1.1.esp