After days of viewing museums, palaces, and churches, go to Hyde Park. In Spring or Summer, rowing or paddling along the Serpentine (natural lake), is really delightful. There is even a swimming area. You might come upon a band giving a concert; an orator in Speakers Corner; the Princess Diana Memorial Fountain. For some other ideas(in a slideshow), see: http://www.frommers.com/slideshow/?p=1&group=503&cat_cd=ARTCULTURE#slide