This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.

A sacred lake with thousands of sacred carp and a biblical history.

Mausoleum and Holy Seat of Antiochus I of Commagene.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

Standing proud atop a Turkish bluff, this Ottoman palace has retained its grandeur despite being abandoned for centuries.

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

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

An abused and forgotten metropolis, abandoned for centuries.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

This column celebrates Rome's victory over the Goths, and may be the oldest Roman monument in Istanbul.

Ancient serpentine sacrifice holder that has stood the test of time.

A medieval bridge stretches over a sulfur-rich river that leads to year-round natural hot springs.

The two abandoned overpasses are among the largest bridges in Poland.

A tribute to the first human in space.

Built to transport German U-boats through the never-completed Masurian Canal, the locks near this Polish village are now home to a rope course.

An impressive monument to Poland's independence.

A cluster of headless, armless sculptures looms within a popular Polish park.

This towering statue of Jesus provided internet to the surrounding area.

A small granite monument marks where the borders of three countries meet.

The site of one of the largest prison escapes of World War II.

These mechanical goats first battled it out in the year 1551, all because of an overcooked deer.

A memorial to the beloved brown bear that served in the Polish army during World War II.

St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.