Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

Where condemned pirates met their grisly end at the gallows on the River Thames.

Revel in the Victorian splendor of the world's oldest eating establishment inside a museum.

Following the trail of an old metro line, this scenic path is haunted by a creepy spriggan statue.

The London pub overlooks where the Mayflower was moored before setting sail for the New World.

A network of concealed passageways lies within a busy London Underground station.

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

Remnants of a Victorian garden feature sitting in public woodland.

Rebuilt remains of a temple to Roman god Mithras.

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

This real life asylum of horrors is now an abandoned ruin that hides the unbreakable code to one patient's insanity.

This 21st century cabinet of curiosities includes dinosaur bones, moon rocks, film memorabilia, and more.

Romans built the world's tallest artificial waterfall in 271 BC.

South of Bologna, a limestone grotto with a protruding waterfall and a floor full of cave pearls.

Renaissance villa and gardens complete with a tormented colossus.

Ancient, mysterious stone altars are hidden among wild woods in central Italy.

"Stairs of the Turks", a chalky white cliff eroded conveniently into stairs, allowing for easy pillaging.

A dreamlike medieval church dug into the tuff rock, with unusual carvings and possible traces of the Templar knights.

This archaeological site built into a tuff outcrop is filled with rock dwellings, the ruins of a medieval castle, and a necropolis.

Leonardo da Vinci was one of many to find inspiration in this unique, rocky landscape in Tuscany.

A series of caves, tunnels, and wells filled with fascinating figures and symbols.

This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

Naturally preserved bodies are eerily staged throughout the crypt in varying poses.