Folly is also a synonym for foolishness; see stupidity. A folly is a silly error.
In architecture, a folly is an extravagant, useless, or fanciful building, or a building that appears to be something other than what it is.
The term comes from the fact that such structures have often been dubbed "[name of architect or builder]'s Folly", in the sense of foolishness or madness.
Follies are usually found in parks or large grounds of houses and stately homes; they may sometimes have been deliberately built to look partially in ruins. They were especially popular from the end of the 16th century to the 18th century.
The Parc de la Villette in Paris has a number of modern follies by different architects.
Fonthill Abbey, Wiltshire, England The Folly Tower at Pontypool, Wales Severndroog Castle, Shooter's Hill, south-east London Rushton Triangular Lodge, Northamptonshire (16th century) Stowe School, several follies in the grounds The Ashton Memorial, Lancaster, England Broadway Tower, The Cotswolds, England Hawkstone Park, follies and gardens in Shropshire, England King Alfred's Tower, Stourhead, Wiltshire, England Williamson's tunnels, probably the largest underground folly in the world, Liverpool, England Flounder's Folly, Shropshire, England The Dunmore Pineapple, Falkirk, Scotland McCaig's Tower, Oban, Scotland Portmeirion, Wales Watkins' Tower, London Bettisons Folly, Hornsea, England Sway Tower, New Forest Old John, Bradgate Park, Leicestershire, England
Désert de Retz, folly garden in Chambourcy near Paris, France (18th century)
The Bomarzo Gardens
Belvedere Castle, Central Park, New York Lucy the Elephant, Margate City, New Jersey Winchester Mystery House, San Jose, California Ypsilanti, Michigan water tower