Cool off this summer at the Serpentine. Located in Hyde Park, the Serpentine Lido is open from 10am to 6pm seven days a week. A concession ticket is just £3.50 and gets you access to the sun terrace, bathing area, and open water swimming in the serpentine.
There is the Lido Cafe with waterside tables. The nearby Serpentine galleries house two contemporary art exhibits that are absolutely free.