The Black Door

In, the Black Door is the entrance to the Falkreath Sanctuary. In, it is the entrance to the Cheydinhal Sanctuary. Both require a passphrase. The former answer is: Silence, my brother, and the latter is Sanguine, my brother. Answering the latter incorrectly results in the door replying, "You are not worthy," The correct response is not an option until the Dragonborn learns it during either the Destroy the Dark Brotherhood or With Friends Like These... quests. Answering the former does not become available until the Hero of Kvatch completes their first contract for Lucien Lachance.