Nine hundred years ago, this was the home of a feudal lord. Today all that remains is a steep mound surrounded by a deep moat.

A circle made up of 19 boulders has stood in Scotland's Bladnoch Valley for some 4,000 years.

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

These ruins witnessed the final gathering of the failed Jacobite Rebellion.

This fortified L-shaped tower is the ancient seat of clan Hannay.

The remnants of a classic 1970's British film.

A gap marks the spot where a now-missing stone once completed the circular arrangement at this Neolithic site.

Named after a 6th-century saint, who was also a scholar.

This bronze sculpture on a former squash court marks the secret origins of the Atomic Age.

This former hydraulic laboratory is now a woodland dotted with old engineering models.

Invisible bridge parts the waters, invoking biblical images and preserving the ominous feel of an ancient moat.

Hidden within a Netherlands crater is a stone bed that lets those who lie in it see the sky as a curved surface.

This disused boat elevator was saved from the scrap heap so that visitors could tour its rusting skeleton.

Museum in a swimming pool where the water still flows.

One of the largest mines in Bulgaria is now home to a vast museum more than 100 feet underground.

An oddly shaped tower built to mark the acquittal of Admiral Keppel in a controversial 1770s case.

A section of a historic wooden trestle viaduct is preserved next to the railway line it once carried.

This tribute to Sunderland's mining past stands outside the home of its football club.

The remnants of this unusual bridge await an uncertain fate.

Its impressive still-working beam engine is a thing of beauty for engineering history fans.

Following years of secrecy, the hidden history of a World War II site is being brought to light.

A blunder resulted in these charming stone-lined streams becoming the target of a Nazi bombing.

In the ancient Woolley Woods, an art project promises access to new worlds.

Cycle the solar system—from the sun to Pluto—right here on earth.