Folly

A name given to any costly structure considered to have shown folly in the builder,

- Shorter Oxford English Dictionary

But it's much, much more than that. The folly, particularly in Britain, is an attitude, a statement, a style, a fashion, a passion, a different world. . .

Follies may be found all over the world, but the British were first to recognise their worth and importance. . .

Gwyn Headley and Wim Meulenkamp have spent over thirty years reasearching 'rogue architecture'. They are co-founders of the Folly Fellowship.

Above text taken from the blurb on the back cover of Follies Grottoes and Garden Buildings by Headley and Meulenkamp, Aurem Press, 1999

Experience, n. The wisdom that enables us to recognize as an undesirable old acquaintance the folly that we have already embraced.
Ambrose Bierce (1842 - 1914), The Devil's Dictionary

Childhood, n. The period of human life intermediate between the idiocy of infancy and the folly of youth - two removes from the sin of manhood and three from the remorse of age.
Ambrose Bierce (1842 - 1914), The Devil's Dictionary.

Other: CORPORATION, n. An ingenious device for obtaining individual profit without individual responsibility.
ECCENTRICITY, n. A method of distinction so cheap that fools employ it to accentuate their incapacity.
IMAGINATION, n. A warehouse of facts, with poet and liar in joint ownership.
INVENTOR, n. A person who makes an ingenious arrangement of wheels, levers and springs, and believes it civilization.
OPPORTUNITY, n. A favorable occasion for grasping a disappointment.
PLAN, v.t. To bother about the best method of accomplishing an accidental result.

folly
One entry found for folly.
Main Entry: fol·ly
Pronunciation: 'fä-lE
Function: noun
Inflected Form(s): plural follies
Etymology: Middle English folie, from Anglo-French, from fol fool
1 : lack of good sense or normal prudence and foresight
2 a : criminally or tragically foolish actions or conduct b obsolete : EVIL, WICKEDNESS; especially : lewd behavior
3 : a foolish act or idea
4 : an excessively costly or unprofitable undertaking5 : an often extravagant picturesque building erected to suit a fanciful taste

Merriam-Webster Online Dictionary:
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=folly

Folly n. a popular name for any costly structure considered to have shown folly in the builder.
Oxford English Dictionary

Folly n. silliness or weakness of mind: a foolish thing: sin: a monument of folly, as a great useless structure, or one left unfinished, having been begun without a reckoning of the cost. To act with folly. Origin French folie – foolish.
Chambers English Dictionary