The granddaddy of English geoglyphs dates back to the late Bronze Age.

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

The stately remains of Llywelyn the Great's mighty fortress.

A hermit's tiny cell built into the cliffside that saved him in South Pembrokeshire.

This foolish Victorian sea fort was converted to a deluxe hotel.

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

Charles Babbage's proto-computer, painstakingly brought to life.

Old-fashioned knowledge and modern engineering create the world's only rotating boatlift.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

This haunting stone chasm is a hotbed of mossy rock and English legend.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

A 6th-century stone lies at the site of the mythical battle waged between King Arthur and his nemesis Mordred.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.

A subterranean playground in an abandoned slate mine.

A unique waterfall that some believe attracts the fairfolk.

The largest greenhouse in the world is home to over one million types of plants.

400-year-old garden, restored to beauty.

A fantastic castle rumored to be the birthplace of King Arthur.

Every year locals tumble 650 feet down to the bottom of the hill chasing a Double Gloucester cheese.

A Welsh sheep farm provides daily (non-sheep) meals to red kites, producing dazzling displays of aerial acrobatics.

One family's environment-friendly hobbit-house in Wales.

This bridge is the first to be made entirely from iron, but designed like it was still made of wood.