folly -
the quality of being rash and foolish; "trying to drive through a blizzard is the height of folly"; "adjusting to an insane society is total foolishness"
folly -
Thoughtless action resulting in tragic consequence.
folly -
A fanciful building built for purely ornamental reasons.
Wikipedia
A folly is a building constructed primarily for decoration, but either suggesting by its appearance some other purpose, or merely so extravagant that it transcends the normal range of garden ornaments or other class of building to which it belongs. In the original use of the word, these buildings had no other use, but from the 19th to 20th centuries the term was also applied to highly decorative buildings which had secondary practical functions such as housing, sheltering or business use. In the 18th century English gardens and French landscape gardening often featured Roman temples, which symbolized classical virtues or ideals.
