The Princess Diana Memorial Fountain, which took an extraordinarily long amount of time to build, is located in Hyde Park. I was in London for 16 hours waiting for my connection flight... so... where would I go but here? This is actually on the very day of the second bombings in London. So you could only go as far as Knighsbridge on the Underground...
It is a very nice fountain, and when you see it you don't really care that it took so long to build. Even though it wasn't a particularly warm day, there were children playing around the fountain. It is a very peaceful place.