Some of London’s best sights are best seen from the relative safety of the upper deck of a bus. (Josie Portillo/for The Washington Post)

I have loved many buses. The one I loved most was the Catbus from the Japanese anime film “My Neighbor Totoro,” which, sadly, I have never had the pleasure of encountering in real life. Transport for London’s Route 139 is a close second.

I love the panoramic view from the front seat of the upper deck. I love the bright lights that make the bus feel like a safe haven when it picks you up from a cigarette-strewn street at 3 a.m. I love how it transforms my simple commute into an appreciation of the interlocking wonders of the city. Rocketing through the London on the Underground might be faster, but gaze out your window on the Tube and you’re met only with your own tense reflection staring back.

The 139 starts (or ends, depending on its direction) in West Hampstead, snakes down past Kilburn, passes monstrous high-rise flats (one with the delightful name “Snowman House”) and then glides down Abbey Road. That’s the Abbey Road, where entrepreneurial types in ­high-visibility vests wave at the buses and cars to slow down so they can charge tourists to be photographed in endless iterations of the Beatles’ iconic crosswalk shot.

The procession of fans at Abbey Road Studios rarely slows the progress of the 139, however, which rolls through St. John’s Wood, then goes down Baker Street, where at the approximate location of 221B a man costumed in deerstalker cap and cape herds chaotic lines of tourists into some semblance of order.

Next, the artful window displays and colossal columns of the mammoth department store Selfridges welcome you to the shopping bonanza (and air-pollution nightmare) of Oxford Street. During rush hour the red buses are packed bumper to bumper. The gridlock is exacerbated by pedicabs, whose drivers spend 80 percent of the time yelling at pedestrians to try to convince them to take a ride and 20 percent moving at a crawling pace directly in front of buses full of angry commuters, who silently will the driver to just go ahead, give in, squash the stupid pedicab.

Riding a double-decker bus makes you feel like an urban mahout. From your perch on the 139 you see swarms of people walking down Oxford Street, all of whom appear to be moving faster than you are. School groups, extended networks of fashionistas, elderly ladies pulling rolling shopping bags, babies swaddled in strollers constructed of more protective Kevlar than military trucks.

And this is just on a regular weekday: During the Christmas season (which in London starts in October and isn’t fully purged until halfway through January) the seas of humanity grow so dense that it is dangerous even to attempt forward motion on foot. Yes, there are reasons to visit Oxford Street during Christmas, when the department stores put up dazzling displays, trees are hung with electrified icicles, and orbs of light are strung sparkling across the street. All of that is glorious, spirit-lifting and definitely best seen from the relative safety of the upper deck of a bus.

The 139 turns away from Oxford Street at Oxford Circus and proceeds along Regent, a continuous curve of neoclassical arches, to Piccadilly Circus, where people sit under the blinking neon signs, exhausted and overwhelmed after queueing for hours to get tickets to “Les Miz.” Eventually the bus rounds a corner and, miraculously, Trafalgar Square appears. Even though the National Gallery and Nelson’s Column are emblazoned on a million T-shirts, tea towels and tchotchkes, it’s still an exciting jolt to realize they’re just there. All the time. For you to pass casually, on the bus, on your way to somewhere else.

With Trafalgar Square receding into the distance, the 139 travels down the Strand and crosses the Thames at Waterloo Bridge. There are many bridges in London, plenty more famous than Waterloo Bridge, but it is Waterloo Bridge that I think offers the best views. To the west you can see the glass pods of the Eye turning slowly, the spiky figure of Westminster, and Big Ben gleaming at night like a second moon. To the east, there’s the dome of St. Paul’s Cathedral and all the glittering skyscrapers that signal the newest era in London’s ancient and enduring history.

When you finally arrive at Waterloo Station itself, there is the entirety of the South Bank, with its theaters, used-book stalls and pop-up restaurants for you to explore.

Or you can get off, cross the street, and get back on the 139 in the other direction.

Kelly is a freelance writer.

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