I found the Boethia shrine in the mountains, and it has an alter of sacrifice, which lights up when you stand on it, but when you click to activate it, it does nothing. I tried dragging a wolf halfway up the mountain to put on it, but no luck. Also tried placing random junk on the sacrifice alter, as well as casting multiple magic spells and searching the camp for clues. Anyone done this shrine and know what to do?

Req is level 30

Source: official guide.

no cultists there?

they will tell you, that you have to sacrifice a follower
you get a dagger to equip, and tell your follower to use the altar, then stab him
he will be lost
i hired someone in a taverne for that

Well no, the only cultists I saw were shriveled up, burned corpses lying on the ground or kneeling. But since I apparently need to be level 30, maybe they will only appear after then.

Your hireling trusted you! OMFG HOW COULD YOU?!