Try the City Cruise from Westminster Pier down river to Tower Pier. Great views of many of London's attractions. Then walk back via St Paul's Cathedral (free to enter on Sundays), Trafalgar Sguare, Horseguards, the Mall, and Buckingham Palace. A great 'mini-tour' taking about 4 hours. For travel for the day, buy a one day travel card. Only 8 pounds, it can be used on trains, tube, buses and DLR after 10.00am. Also gives good discount on City Cruise prices. Anyone needing any help, feel free to contact me at mike@gal.ac I have no vested interests, just happy to help if I can. Mike