Probably there is no single definition of a folly that fully encompasses all its elements. However, the following may collectively give some idea of what is meant by the term folly:

• “building without practical purpose”
• “a garden building constructed mainly for visual effect”
• “an extravagant, useless or fanciful building that appears to be something other than what it is”
• “a building in the form of a small castle, temple, etc, that has been built as a decoration in a large garden or park”
• “a great useless structure, or one left unfinished, having been begun without a reckoning of the cost”

For further consideration, it is worth visiting http://www.heritage.co.uk/follies/ffdef.html

Sources

Ammerdown – Little and Aldrich (1977)
Follies, Grottoes and Garden Buildings – Headley and Meulenkamp (1999)
Follies and Grottoes – Jones (1974)
Follies magazine (in particular numbers 16, 21, 30 & 41)
Lighthouses – Pearson (1995)
Lighthouses: their architecture, history and archaeology – Hague and Christie (1975)
Lighthouses of England and Wales – Jackson (1975)
Peter Scott – Huxley (1993)
The Lighthouse Stevensons – Bathurst (1999)
Henry Winstanley and the Eddystone Lighthouse – Hart-Davis and Troscianko (2002)
Lundy – Langham (1984)
Rock Lighthouses of Britain – Nicholson (1983)
An Historical Account of the Medicinal Waters or Mineral Springs of Daviesville at Burnham near Bridgewater – Henning (1836)
Somerset Curiosities – Byford (1989)
Country Life (2 March 1929)
Manchester Evening News (22 April 2005)
Sunday Express (14 August 1994)

Acknowledgements