221b Baker Street was the London residence of the famous literary detective Sherlock Holmes, created by author Sir Arthur Conan Doyle. The number followed by a letter is a separate number in law and indicated an apartment on the 1st floor (US-2nd floor) of a residential lodging house that was likely to have formed part of a Georgian terrace.

The site of the house has been much disputed by scholars, although the address did not exist at the time when the stories were first published in 1887.

          “We met next day as he had arranged, and inspected the rooms at No. 221b, Baker Street, of which he had spoken at our meeting.  They consisted of a couple of comfortable bed-rooms and a single large airy sitting-room, cheerfully furnished, and illuminated by two broad windows.”      -Arthur Conan Doyle, A Study in Scarlet, 1887