With Friends Like These...
How To Unlock: Join the Dark Brotherhood.
Finding the Dark Brotherhood is as tricky as it sounds, but not anymore. I'm not entirely sure how I got this into our miscellaneous objectives, but I did and if I recall correctly, it was from asking bar tenders rumours about the region. When you find the right barman, although you could probably go right to the house, you’ll have to find a boy called Aventus Aretino who can be found in the Arentino Residence in Windhelm. Speak to the boy, complete the “Innocence Lost” quest and then sometime shortly after a courier will give you a note saying “We Know.” Then just sleep, you know the score with the Dark Brotherhood if you played Oblivion.