Parliament Hill Lido, Hampstead
If you don't fancy the Hampstead Heath's bathing pond water, then you don't have to go far for a dip. Sitting on the edge of the heath, the heated lido pool is 200ft long, 90ft wide - perfect for getting some pretty serious strokes in, at least outside of the school holidays. Throw in a great 1930s café and it becomes a fantastic summer chill-out spot.
Gordon House Road, Hampstead, NW5 1QR. Call 020 7332 3773.