In the underdark, there was that cave with the Kuo-Toa in it. There was a big room with statues of mind flayers, and some demon. It wanted an animal sacrifice to realess the "five" or something. Just wondering what that was about. When I was down there, I never came accross such a thing, and for the life of me, I don't remember anyone else speaking of it.

Spoilers

The 'five' it releases is five demon knights (just cast animal summoning and move them near the statue). One of them has some nice armour, a nice sword and a girdle which is needed for the crom frayr.