See gorgeous frescoes at this modest Byzantine place of worship.

After witnessing the rise and fall of three empires, this ancient city was finally destroyed by a series of earthquakes.

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

A naturally beautiful, seemingly bottomless deep blue spring.

St. John the Baptist's forearm is housed in this remote 11th-century monastery.

This fortress dates back to the 6th century and is also the site of a controversial abandoned restoration project.

Artists made this mosque into a marvel of Ottoman baroque architecture.

This 3,800-year-old site contains markers used to study the movement of the sun and moon and create a lunar calendar.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

The Pope’s secret escape route.

Designed by the architect who also had a hand in crafting the Westminster Abbey and Bristol Cathedral.

A museum that chronicles the interesting and often dark history of the London docklands, once one of the major trading ports of the world.

Eighty million natural history specimens call this gargantuan museum home.

An unusual round church in London with a Templar past.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Hidden behind a wall for decades, this masonic lodge was only rediscovered during renovations.

Artists and musicians now rule over this former rail station.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

This beautiful Victorian ironwork masterpiece was built to keep London from smelling like poop.

Pop culture has helped to keep this iconic British building from being destroyed.

This home on a quiet suburban street is completely covered with vibrant mosaics.

The spectacular and eerie moss-covered grave site of 19th-century Belgian merchant.