And now the Bakerloo heads south, beneath Portland Place. This is one of the most elegant streets in London, although it would have been even grander had architect John Nash had his way. He planned a processional thoroughfare for the Prince Regent, leading from Carlton House on the Mall to the prince's summer villa in Regent's Park. It was to be a straight line, but land battles with Sir James Langham and the residents of Cavendish Square forced part of the road further east than Nash would have liked, creating a distinctly imperfect kink around Langham Place (full history here). But the road remains far broader than most, like a Georgian dual carriageway, and is always a impressive place for a quiet stroll. Here are some of the architectural (and other) treats to be seen down Portland Place:
• Park Crescent: One of Nash's first crescents[photo], originally planned as a full circle (or circus). The purity of its white stone colonnades still makes me think that Mary Poppins is about to fly in at any minute.
• Several statues down the 'central reservation': A real mixed bag, including Joseph Lister (who pioneered the use of antiseptics in surgery - pictured), SirGeorge Stuart White (Boer War commander) and QuintinHogg (founder of the first polytechnic).
• RIBA: The headquarters of the Royal Institute of British Architects is a sheer stark slab of 30s brutalism [photo]. On the pavement outside there's usually a poignant one-woman protest aimed directly across the road at the Chinese Embassy (read more here).
• Lots of scientific associations: The largest of these is the Institute of Physics, but there's also the Royal College of Radiologists, the Institute of Chemical Engineers and my personal favourite, the Anaesthaesia Heritage Centre. No, really.
• BBC Broadcasting House: About which I wrote in depth when I went for a tour last year. The interior of the building is still being renovated, but it looks like they've pretty much finished the exterior at last. The Bakerloo line passes very nearly underneath the building, which used to cause all sorts of sound problems when certain radio programmes were being recorded, but the latest design features heavy soundproofing throughout. There's an outstanding history of the site here, of the original building here and of the new development here.
• The Langham Hotel: London's first purpose-built grand luxury hotel, originally with 600 rooms (now 427). Famous regular visitors included Oscar Wilde, Mark Twain, Noel Coward, Antonin Dvorak and Haile Selassie. 100 years ago a room cost 9 shillings (45p) a night - today that's merely an insulting tip. Full historical trivia here.
• All Souls, Langham Place: John Nash's signature circular church, with the famous lemon-squeezer roof and spire [photo]. Inside there's perhaps more a feeling of theatre than temple, but that's perfectly in keeping with this modern church's vibrant outreach ministry. How many other churches allow you to download their last four weeks' sermons?
Baker100 walk: Regent's Park to Oxford Circus
• Park Crescent: One of Nash's first crescents [photo], originally planned as a full circle (or circus). The purity of its white stone colonnades still makes me think that Mary Poppins is about to fly in at any minute.
• Park Crescent: One of Nash's first 