The traditional old-style red double-decker buses (with a conductor and an open platform at the back) were a much-loved part of London life, so when they were phased out in 2005 lots of people were aghast. Luckily, the Mayor decided to keep a few of the old 1960s buses running on two special 'heritage routes'.
So how about forgoing the tube for a day, and taking a ride on one of London's old buses?
The first route is called No.9, and runs between Trafalgar Square and Kensington High Street:
Trafalgar Square --> Piccadilly Circus --> Piccadilly --> Hyde Park Corner --> Knightsbridge --> Royal Albert Hall --> Kensington High Street
The second route is called No.15, and operates between Trafalgar Square and the Tower of London:
Trafalgar Square --> Strand --> Fleet Street --> Blackfriars --> Mansion House --> Cannon Street --> The Monument --> Tower of London
Craig has written a review of the No.15 on his blog, if you'd like to get an idea of what it's like. Feel free to ask him a question about the bus. He actually recommends catching the No.11 instead, which is a lot more interesting (it's not a heritage bus -- but it's a much better sightseeing tour). He's also put together a marathon bus journey around London which strings together lots of different bus routes, so you can see lots of London landmarks.
Important note: The heritage routes operate between 9.30 AM and 6.30 PM. Modern buses also operate on the same route, using exactly the same bus numbers, but with extended hours and routes -- so make sure you board the right one. The heritage buses have an open platform and staircase at the back. If you want to see some real old buses (even older than these heritage ones), then check out the exhibits at the London Transport Museum.
Because these heritage buses are just normal everyday buses, you can still pay with an Oyster card, Visitor Oyster card, contactless card or travelcard. They don't have any Oyster machines inside, though (those big yellow things that you tap the card down on). They have an old-fashioned conductor instead, with a hand-held machine. So all you have to do is sit down and show him your card when he approaches. Sometimes he's a bit lazy and will just stand by the bottom of the stairs instead, so you have to show him your card as you board, or when you get off.
If you enjoy sightseeing bus tours in London then you might like these other London events…
Ghost Bus Tour, around London’s dark past – Every day
See London by night — on a sightseeing bus – Every day
The Original Tour — Open-top sightseeing bus – Every day
London Bus Tour — open-top sightseeing bus – Every day