London's number 9 route runs from Hammersmith in west London to Aldwych in central London. The route is served by a new Routemaster bus, an updated version of the classic red double-decker bus.
The route takes you past several London landmarks like Trafalgar Square, the Royal Albert Hall and Kensington Palace.
Check out the full list of London Bus Routes For Sightseeing.
An Oyster card, or a one-day travelcard makes all buses (and tubes and London trains) a hop on/hop off service.
The No. 9 London Bus
Time needed: Approximately one hour
Start: Hammersmith Bus Station
OK, jump on the bus and try and get a seat upstairs at the front for the best views. Within a few minutes you'll be on High Street Kensington and there are lots of shopping opportunities.
Just off the main road is 18 Stafford Terrace although you won't be able to see it from the bus. There's also the wonderful Kensington Roof Gardens high up on the right but I don't think you can see it from the bus either. It is worth calling ahead though to see if the gardens are open as they are free to visit.
Within 5 minutes you should reach the bus stop for Kensington Palace. (Do note, the bus stop is actually before you can see the palace.) If you stay on the bus you'll catch a glimpse of Kensington Palace on your left as well as Kensington Gardens.
A few minutes further and you'll see the Royal Albert Hall on your right and the Albert Memorial on your left.
Then look to the right again to spot an old milestone. It's on Kensington Road (the road the bus is on), near the junction with Exhibition Road, outside the Royal Geographical Society.
After this junction the park on your left changes from Kensington Gardens to Hyde Park, although it doesn't really look any different.
As you continue along Kensington Road you'll soon pass the Kensington Barracks on your left, the home of the Household Cavalry.
At Hyde Park Corner there is Wellington Arch in the middle of the roundabout and, after the bus stop, on the left is Aspley House which was once called Number One London.
On the Hyde Park Corner island you may also spot the New Zealand War Memorial. It's 16 cross-shaped bronze 'standards' on a grassy slope. It commemorates the enduring bonds between New Zealand and the UK.
The bus now goes along Piccadilly and the original Hard Rock Cafe is on the left. In the shop you can also visit The Vault full of rock memorabilia.
The area on your left is Mayfair and on your right is Green Park, which has Buckingham Palace on the other side but you won't be able to see across. As the bus continues along Piccadilly look out for the Athenaeum Hotel living wall on your left.
At the Green Park tube station bus stop you can see The Ritz Hotel on the right.
Look ahead to the end of the street and you should be able to spot the Eros statue at Piccadilly Circus.
Apparently it's actually the Greek god Anteros, the brother of Eros, but no-one calls it that.
Just after The Ritz, there's The Wolseley which was once a car showroom but is now a lovely restaurant.
Next the bus turns right down St James's Street and you have St. James's Palace straight ahead at the end. On the left look out for JJ Fox, which has a Cigar Museum in its basement, and Lock & Co Hatters, which was founded in 1676.
Take a quick look to the right at Waterloo Place to see Duke of York Column before the bus soon reaches Trafalgar Square and goes along the southern edge of the Square. Have a good look to your left to see Nelson's Column, the fountains and the National Gallery along the north side.
The bus journey continues along the Strand and Charing Cross station will be on your right. Notice the Eleanor Cross in the station forecourt.
After the Southampton Street/Covent Garden bus stop (Covent Garden is on your left) get ready to spot The Savoy Hotel on your right. Look ahead for The Savoy Theatre signs which can be seen from the Strand but the hotel is set back.
Before the bus gets to Aldwych have a quick look over Waterloo Bridge and then Aldwych/Drury Lane is the last stop.
On the other side of Aldwych near the junction of Surrey Street and the Strand you can see the most famous disused tube station, Aldwych station, and take a look at London's Roman Baths. You could walk into The City from here along Fleet Street but most people will probably want to head into Covent Garden so from the bus stop, walk up Drury Lane and turn left at Russell Street to reach the piazza.