One of the stations on the original underground line.
Lines using the station - Metropolitan Line, Circle Line, Hammersmith and City Line, Bakerloo Line and Jubilee Line. Above the station is Chiltern Court and outside the station is a statue of Sherlock Holmes.
Nearby are Madame Tussauds, the Sherlock Holmes Museum, London Zoo and Marylebone Station.
The Wikipedia page is [1] and the TfL page [2]. A video here.