A surprising and unconventional mosque hidden in the subsoil of Istanbul.

A meow-velous tribute to a beloved street cat, made famous on the internet.

An Ottoman-era mosque looking over the Black Sea.

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

One of the newest mosques in a city filled with thousands.

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

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

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

Byzantine emperors ruled, lived, and died in this 13th-century palace-turned-museum.

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

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

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

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

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

A tiny park in the middle of some big power politics.

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

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

A fountain standing as a testament to a doomed alliance.

A marvel of Byzantine engineering under the streets of Istanbul.

This modest marker near Notre Dame identifies the very center of Paris.

If you look closely at the oldest bridge in Paris, you might notice hundreds of ugly faces leering from its sides.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The celebrated eyesore created by starry-eyed sweethearts.

This bridge was constructed from the rubble of the infamous Bastille.