The Hop on Hop off buses are a great way to see London and you have the option of a river cruise too included (should you want it) in your ticket. There are several companies Big Bus, Toot Tours, Top View Tours and Golden Tours - they all pretty much do the same thing and you can hop on hop off as many times as you like at any of the attractions. You then board another bus (they run every 10-30 mins) whenever you're ready.

For the river cruise, this runs from Westminster to the Tower of London or vice versa. The hop on hop off buses are a great way to explore London and seeing the sights.