Board Thread:Skyrim/@comment-108.90.253.239-20150604193552/@comment-6881629-20150604201158

To get The Whispering Door you must be level twenty or over and have done the main quest  Dragon Rising, you get the quest by asking for rumors from Hulda the innkeeper of The Bannered Mare (and only her). You might have to ask her a few times to get the dialog that starts the quest (especially if your a vampire as you get the cure quest in a similar way).

If your on PC and have no luck try the console command -

setstage DA08 10