These abandoned coal mine towers near Sherwood Forest might soon boast the U.K.’s longest zip-line.

One of London's lost rivers runs through a pipe over the tracks of this subway station.

A petite castle folly in the English countryside.

An intriguing three-sided folly is a testament to one man's devotion to Catholicism and the number three.

A lavish Victorian mansion wound up inheriting a gruesome reputation that would be its demise.

One of Scotland's most important modern structures, it just made the '100 Most Endangered Sites' list.

This lone tower casts an outstretched shadow over the site of a once-wealthy Knights Templar preceptory.

Exquisite carvings of leaves, Green Men, and the occasional dragon adorn a medieval chapter house.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

A beautiful Kentish country intersection hosts a tasty little photo spot.

This muddy wooded valley and the ancient structures it hides are said to be the favored haunt of the legendary Friar Tuck.

This strange seaside tower got its name from a wealthy eccentric who would hide coins among its stones.

Remnants of a Victorian garden feature sitting in public woodland.

This lonely metal cross may hint at the true location of a medieval showdown between Christian and Pagan kingdoms.

How did a literal hole in a wall become one of the top-rated tourist attractions in this English town?

A well preserved remnant of the English Civil War.

One of the earliest large-scale "hyper" roofs in the U.K. is now a derelict roadside attraction.

This 600-year-old tower was built as a comfy residence for cherished pigeons.

These bleak 800-year-old ruins were once the royal residence of choice for hunting in Sherwood Forest.

This romantic, decaying 13th-century ruin on the edge of Sherwood Forest is reputedly one of England's most haunted places.

An abandoned, desolate train tunnel that was used during World War II.