Sacellum of Boethiah

Sacellum of Boethiah is a shrine, west of Windhelm, with a unique "Sacrifice Stone" on the shrine. Upon first arrival (~lvl15) nothing seemed to happen. Revisiting (~lvl30) there were a Cult of Boethiah at the entrance, demanding you to gain someone's trust and to bring them to the shrine to summon Boethiah herself. Upon bringing a house arl (Lydia, ect.) you can command them to touch the shrine, thus allowing you to sacrifice them and summoning Boethiah who gives you the quest Boethiah's Calling.

The first part of the quest is to be the last person standing in the area.

The second part is to kill her previous champion at Knivepoint Ridge "stealthly".