Some of London's most thrillingly situated bike racks are here, on the Thames Clippers fast ferries. They're commuter services, but take bikes (though we've never seen any, apart from ours).
For sightseers, the £12 rover tickets give you unlimited travel on the Clippers all day after 10am, from O2 in the east to Millbank in the west.
Both the O2 and Tate Britain have some of the free ping pong tables set around London this summer - they'll be taken down after this weekend, so hurry.)
Talking of hurrying, the best bits are east of Tower Bridge, where the boat bombs along like Donald Campbell in Bluebird just before closing time. If you do put your bike in the racks, it might be an idea to lock them, just in case.