Dictionaries try to pin down a precise definition of what a folly is, when the beauty of them lies in their very unpredictability. A few of them are useful, many are merely decorative, some simply make you stop and puzzle over why anyone bothered.
Nearly all can be viewed from one angle as a waste of money, and they're all different to each other. A folly is in the eye of the beholder, say Gwyn Headley and Wim Meulenkamp in their definitive guide to British follies Follies, Grottoes and Garden Buildings (now sadly out of print).
They maintain that a real folly builder will deny that he ever intended to build a folly. Folly , these experts say, is a title only other people can bestow on your whimsical structure.
Wales has a grand-scale folly in the shape of the other-worldly village of Portmeirion; Scotland has many, including an odd version of the Coliseum near Oban and The Pineapple at Dunmore Park; in Suffolk The House in the Clouds suggests in the distance that it just floated down from The Land of Oz; and Yorkshire is littered with follies, including The Rocket Ship in Wensleydale and The Temple of the Four Winds at Castle Howard.
In Leeds, Roundhay Park's ruined woodland castle is a folly, as is the strange Bear Pit on Cardigan Road in Headingley. Back in 1710, the Earl of Carlisle's whimsy must surely have been secretly sniggered at by some, when he commissioned the great Sir John Vanbrugh, architect of Castle Howard, to design an ornamental stone well cover in honour of Robin Hood, which can still be seen in a layby off the A1 not far from Burghwallis near Doncaster.
"Generally, they're meant to be 'eyecatchers', says Giles Proctor, historic buildings architect at English Heritage, which has helped to restore many of Yorkshire's finest follies. Most of them have been built by wealthy people as architectural recreations, going way beyond what was strictly necessary for everyday living. Some have a theme, and some are tributes to a person someone wished to flatter – such as the Queen Anne Obelisk and Duke of Argyll Column at Wentworth Castle near Rotherham.
Follies tend to spawn folklore, and one such example is the Temple of Victory on the Allerton Castle Estate close to the A1 near Knaresborough. Situated on top of its own mound, the Grade II* listed building is an elongated octagonal summer house built by James Payne in the Palladian style.
Its three projecting balconies give views of Drax power station, Almscliffe Crag, York Minster and the North York Moors. All in all its position commands attention, screaming "Look at me! Someone very important lives here!" The most famous person who has lived at Allerton was Frederick Augustus, the second son of George III, who bought the estate in 1786 and later became known as "The Grand Old Duke of York". The hill referred to in the nursery rhyme is said to be the very mound beneath the Temple.
So far no-one has published a book about the hundreds of follies famous and obscure to be found all over Yorkshire. But if anyone is going to it will surely be Karen Lynch from Ilkley. She became fascinated by the scale and lavishness of some of her local follies while growing up in the north-east. "Many are useless, unexplained and romantic, and it often happens that there are completely erroneous stories attached to them", says Karen.
As a girl she was always interested in local history and architecture, and an aunt in London who worked in a bookshop would look out for books that would feed that passion, including a copy of Pevsner's Northumberland. The grounds of Alnwick Castle and Wallington Hall became favourite haunts.
After university, Karen began a career in arts marketing and worked at Opera North then later did historical research on the buildings and gardens at Harewood House. Alongside this she read more and more widely about historic parks and garden,s and began what is now a massive database of information on follies to be found in every corner of Yorkshire.
She's also an avid fan of 18th century travel journals, some of which present new information on follies that she can then chase down for inclusion in her book.
"One of the reasons I've spent more than 20 years slowly amassing the material of Yorkshire follies is that I'm a perfectionist, and it's difficult to say 'right, I have all the right information' because more historical details could them come along and make the book look incomplete.
"Another problem is that I'm too easily sidetracked, but I love doing a variety of work, and do a lot for both The Gardens Trust and The Folly Fellowship". The latter was a discovery of her property developer husband David.
"He came home one day, waving a copy of Building News, and said 'Look, there are more nutters out there like you'. He'd seen an item about the Fellowship, a group of folly enthusiasts who, like me, love research their stories and are happy share information".
She's obviously meticulous in her research, and won't take second or third-hand accounts as kosher.
"I' m not content to settle for information such as 'said to have been built around 1800'. I have to go back to the original sources, such as documents at land registries or builders' accounts in private collections, which involves travelling, a lot, as the documents can be all over the country".
Karen takes on work for other people's books – one current project involves researching the history of three follies overlooking Lake Windermere. There's nothing worse than not being able to find an answer, she says.
"You can get lucky with one folly, such as those at Harewood, and find detailed records of the construction including what each labourer was doing and what each brick cost; yet with others you can find very little."
Follies became more and more fashionable from 1500 onwards, peaking in the 18th century with the development of the landscaped park. They often provided a 'punctuation point' on the landscape at which to stop and admire the house, and some even had a 'necessary house' (loo) at the back for those walking or riding around the grounds.
Other were used for refreshments during an outing or mid-hunt, with servants sent ahead to prepare the table, food and drink.
"They were a means of showing off", says Karen. "They also sometimes gave architects an opportunity to dabble in a new architectural style but on a small scale. Most are just whims and fancies".
Has the building of follies fallen irrevocably from fashion? Not entirely, if the 'mock ruin' kits available on the internet are anything to judge by.
"I suppose a few people do build follies now" says Giles Proctor, "but not on so large a scale, because the cost of building is so much greater. You do see the odd garden temple about. In one form or another human beings still find a way of indulging themselves and showing off their wealth".