In July 2004, the queen came to Hyde Park, probably grudgingly, to open an unusual gated fountain designed to conjure the memory of the mother of her grandchildren and a longtime thorn in her side, Princess Diana. As designed by American architect Kathryn Gustafson, this graceful, O-shaped fountain undulates down a gentle slope, sending two flumes of water gurgling into a collecting pool. At three points, bridges carry you to the center. Rather than putting you in a state of remembrance, it may put you into a state of wanting to ride it on an inner tube. Reach it from the Alexandra Gate at Kensington Gore, Knightsbridge, up Exhibition Road, and don’t confuse it for the Diana, Princess of Wales Playground in Kensington Gardens or the 17th-century Diana Fountain.