folly

In architecture, an eccentric, generally nonfunctional (and often deliberately unfinished) structure erected to enhance a romantic landscape. Follies were particularly in vogue in England in the 18th and early 19th century. They might resemble medieval towers, ruined castles overgrown with vines, or crumbling Classical temples complete with fallen, eroded columns. In the U.S., the term has been applied to ornate gazebos. It may also be applied to any unusual building that is extravagant or whimsical in style.