The outcropping is graffitied with the name of the beloved musical Muppet television series.

On the edge of the Valles Caldera National Preserve, these rock formations create an eerie landscape.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

Mysterious painted skulls in Moravia.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

Submerged trees jut ghost-like out of an idyllic turquoise mountain lake.

Rusting ships sit in a desert where a sea used to be.

World's oldest and largest space launch facility, once a secret missile testing site.

One of the most horrible legacies of the Cold War is a site where the Soviet Union tested nuclear bombs on civilians.

This unique wooden mosque resembling a Chinese pagoda was said to be built without the use of nails.

Mysterious spherical rocks in the semi-desert of western Kazakhstan.

This seaside sanctuary was once one of the most important religious sites for women in ancient Greece.

A magical, if a bit tacky, 1960s castle conjures up medieval fairytales and Greek mythology.

According to legend, this cavern holds the passage that Persephone used to travel to and from the underworld.

This little Greek plateau is home to thousands of rustic, white-sailed windmills.

Overlooking the harbor is a beautiful neglected mansion guarded by two Egyptian sphinxes.

This ancient statue of Dionysus lies unfinished and abandoned in one of Greece's oldest quarries.

A miniature desert appears out of nowhere on the lush isle of Lemnos, like something out of a Greek myth.

A Byzantine-era church hidden in a wooded area below the Acropolis.

The oldest standing Byzantine church in Athens is tucked within a monastery in the middle of an upscale shopping district.

This 13th-century monastery chiseled into the side of a mountain is equipped with a bridge that can be lifted to protect against raids.

This 200-meter-high waterfall marks the site of Achilles’s immortal baptism at the mouth of the River Styx.

The rocky remains of an ancient Greek forest.

What once sat in the world’s spotlight is today a largely disused ghost complex.