Broadway Tower is a folly -- that is to say, a building built just because it could be, to demonstrate the wealth of the owner, and to look cool. It stands on Broadway Hill, in the county of Worcestershire, England. It is, essentially, a castle, although a very small one.
To be clear, it is not a miniature castle, just an abbreviated one. The battlements top out at 17 meters, somewhat shorter than the average English castle but still quite respectable. Particularly so in light of the fact that its base is approximately 12 meters across on its longer axis. It is essentially a hexagonal keep four stories tall, with three towers on alternating corners, all built in the Saxon style. On first glance it appears to be everything a castle should be... Except that most of it isn't there. The effect is rather hard to describe adequately, so I've posted a few links to photos of the tower at the end of this writeup. I high recommend taking a gander at them.
Broadway Tower was constructed in 1799, by George William, 6th Earl of Coventry for his wife. It was designed by James Wyatt, who is perhaps better known for designing The Pantheon and Radcliffe Observatory. There are two stories as to why it was built. The first is that it was intended as a commemorative monument to Admiral Duncan's victory over the Dutch just before the turn of the 18th Century. The other, and more likely, story is that it was simply built to be a beacon, lit when Lord Coventry was returning home from London to alert his staff at Croombe Court, 20 miles away, that he was on his way. Whether or not this was the original reason Broadway Tower was built, it was certainly used this way.
Broadway Tower has served as a holiday home for most of its history. Among the many various transient residents were William Morris (textile designer, artist, writer, and socialist; he designed some of the wallpaper found in the tower), Thomas Phillipps (famed bibliomaniac, who set up his printing press there for a while), Edward Burne-Jones (artist and designer), and Dante Gabriel Rossetti (polymath artist).
These days Broadway Tower is a minor tourist attraction, located in a country park off of the Cotswold Way hiking trail (it is a rather epic hiking trail, being over 100 miles long). You can take a tour for a small fee, although the best photo opportunities seem to be found on the exterior of the tower.
A few pictures of Broadway tower:
Top of the world
And the tower's website, with both interior and exterior shots, and contact information.