Anyone been on a Dinner Thames River cruise ? How was it?
To see if you would like it take the Thames river cruise that goes between the Tate Modern and the Tate Britain. If you like it you can take a longer one.
If you fancy a trip to Greenwich, the oyster card includes a boat ride either to or from. Greenwich is well worth the effort to see all the British naval history and the Prime Meridian where east meets west and the source of Greenwich Mean Time. I suppose you could just take the boat up there and return via train, all on the oyster card. I don't know if the boat ride can be done both ways or not.