The Tallest in the World

At 275 feet, the Wainhouse Tower in Halifax is the tallest folly in the world.
It was designed in 1871 by Isaac Booth to serve as a chimney for John Wainhouse's dyeworks but was never used as one - however it came to serve another purpose.
In 1874 Wainhouse sold his dyeworks, but the new owner refused to take on the expense of completing the tower's construction, so Wainhouse decided to keep the tower for himself and use it as an observatory and viewing platform.   
This decision had the added benefit of irritating his local rival, a landowner named Sir Henry Edwards, who boasted of having the most private estate in the area. When the tower was opened as a viewing platform, it overlooked Sir Henry's estate!
The folly cost £14,000 to build and has 405 steps to the top. It is now Grade II-listed and open to the public only on Bank Holidays.