The northern areas of London, unbeknown to most, have many fine ponds great for a swimming holiday. The Hampstead Ponds and Highgate Ponds date back to the 17th and 18th centuries when 30 ponds were made artificially to serve as reservoirs. Only 3 of them, the very Hamstead Ponds, are good for swimming. Two of them are single-sex, and another is available to anyone. The best season for swimming is from April to October.