Carnaby Street was at the heart of Swinging London in the 60s. John Stephen's famous men's shop on Carnaby Street was a Mecca for the London mods. The whole street was the place to shop for the young and trendy, as satirised in the Kinks' "Dedicated Follower of Fashion". The Jam were less than impressed with the Carnaby Street of the late 70s. They sang "Carnaby Street, not what it used to be". These days Carnaby Street is something of a tourist attraction. However, it is still a great place to shop for mod gear. John Stephen's shop has gone, but there are several other shops taking inspiration from the spirit of the 60s.
To get there from the Americana; take the Bakerloo Line southbound from Baker Street to Oxford Circus. Look for the Argyl Street exit and turn to the left when you get to the street level. You will see Carnaby Street in front of you when you get to the bottom of the street.