Roman ruins top white travertine terraces formed by ancient hot springs.

This 11th-century Greek monastery has renowned mosaics and relics of a brutal past.

This Turkish cave boasts some rather bizarre associations with the King of Mount Olympus.

Cave on extinct volcano, once home to famous mathematician Pythagoras.

This crumbling medieval basilica once attracted pilgrims by the thousands to collect a miraculous dust that formed above the saint's tomb.

The alleged house of the Virgin Mary is tucked away in a park and nature preserve on Mt. Koressos in Turkey and is holy to both Catholics and Muslims alike.

Seven early Christians were sealed into a cave where legend has it they slept unharmed for centuries.

An underground network of massive stone arches and their skylit vaults support ruins of portico structures above.

The only residents of this abandoned housing development full of identical castles are stray cats and dogs.

It's believed that this small church was connected to the Hagia Sophia via a secret tunnel.

An Art Nouveau gem hides beneath the layers of city grime obscuring this once-magnificent building.

A sixth-century Byzantine cistern hidden below a modern carpet store.

A marvel of Byzantine engineering under the streets of Istanbul.

Legend says if you stick your thumb in the hole and it gets wet your wish will be granted.

Quite possibly the oldest love poem known to humankind.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

The ornate miniature mansions were built for Istanbul's feathered residents.

From scholastic to sepulchral - now under reconstruction.

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

You must take the A train... to the last active cemetery in Manhattan.

This derelict building used to house infirm Freemasons, their widows, and orphans.

This abandoned caretaker's apartment is one of 13 left in the New York Public Library system.

Hordes of precariously balanced stone figures crowd the shores of the Hudson River.