An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

One of Europe's oldest libraries.

A meandering boardwalk across the bogland leads to a "stairway to heaven" with sublime views.

A harem-inspired Moorish fantasy design in a Victorian-era Welsh castle.

This magical museum celebrates the life and work of a seminal children's book writer (and occasional spy).

A giant pineapple, a symbol of hospitality, and an amazing vacation rental option.

This observatory within Europe's first dark sky park offers stunning views of the night sky.

St. Mary's Asylum was isolated and abandoned before being converted into a Bed and Breakfast.

A curious collection of mechanical moving figures.

Follow the original medieval paths that wind through this intriguing section of the city.

This modern labyrinth lies in the shadow of a ruined medieval castle.

One of the largest sculpture collections in the U.K. features history's greats, from Bob Dylan to Galileo, in bronze.

This Manchester laundromat is hiding something.

Ruined castle with subterranean vaulted Goblin Ha' or "Goblin Hall."

J.R.R Tolkien, C.S. Lewis, and other "Inklings" met at the Oxford pub to discuss the now legendary fantasy stories they were writing.

This crumbling folly looks like an enchanted left over from Middle Earth.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

A glorious pub known for a spiteful printing feud and its famous typeface lost—then found—at the bottom of the Thames.

A musical composition 1000 years in length plays at the Trinity Buoy Wharf in London.

A house of bones — but nobody is quite sure to whom they belong.

This well-preserved Cistercian Abbey in a romantic pastoral setting has inspired artists like the poet Wordsworth.

A Victorian park cemetery, standing on the site of what was once the Great North Wood.

Besieged by war, this castle ruin has crumbled into a peaceful picnic spot.

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.