To the north and east of Hampstead, and separating it from Highgate, is London's largest ancient parkland, Hampstead Heath, which includes the well-known and legally-protected view of the London skyline from Parliament Hill. The Heath, a major place for Londoners to walk and take the air, has three open-air public swimming ponds; one for men, one for women, and one for mixed bathing, which were originally reservoirs for drinking water and the sources of the River Fleet. The bridge pictured is known locally as 'The Red Arches' or 'The Viaduct', built in fruitless anticipation of residential building on the Heath in the 19th century.