This half-forgotten fortress was constructed by the Ottoman conqueror of Constantinople.

A fountain standing as a testament to a doomed alliance.

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

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

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

The legendary luxury train passage is commemorated with a charming museum inside its former eastern terminus.

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

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

The most metal church of all time was built in record time because of an international, pious pissing contest.

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

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

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

A marvel of Byzantine engineering under the streets of Istanbul.

Khmer Rouge's high security prison.

One of the biggest markets in Asia, under one of the continent's largest domes.

5,000 skulls in memorial to those killed by the Khmer Rouge.

A battle between nature and architecture in the Cambodian jungle.

Over the dunes of the Empty Quarter, the mysterious music of the desert.

This spectacular mosque houses the second-largest chandelier in the world.

This beautifully restored fortification kept the city safe for centuries.

An imposing Omani fortress surrounded by date palm trees.

Nature's water park in the Wadi Bani Awf valley is full of pools flanked with cliffs and natural water slides.

Traditional architecture and ancient irrigation systems are on display in this gorgeous mountain village.