first you need to get the Darkmoon Seance Ring from the Catacombs, located behind the wall you can break, kill skeletons there jump down and retrieve ring. once you reach Anor Lando, if you rotate the rotating staircase all the way counter clockwise, so it goes lower, head all the way down the stairs and head toward the fog door. you will be told to halt. do so, bow kneel on the rug, and join the covenant and the achievement is yours. head thru the fog and you void the trophy