A marvel of Byzantine engineering under the streets of Istanbul.

"Holy Wisdom" overlooks the city that became its namesake.

A striking symbol of the Bulgarian capital.

This historic black and white monastery is one of Bulgaria's architectural jewels.

Neighborhood in Jerusalem is home to the ultra-orthodox haredim.

This daunting 1st century fortress was purportedly the site of one of the most dramatic revolts of the Jewish-Roman wars.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The design of this beautifully crafted building was inspired by Norwegian glaciers.

It houses the remains of a 17th-century version of the Titanic.

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

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Medicinal spa created with the discharge from a geothermal energy plant.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

The picturesque birthplace of Icelandic democracy is drenched in the blood of its brutal past.

This beautiful, historic church looks like something out of a simpler past.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

Just like the real 36th president of the United States, animatronic LBJ amuses visitors with jokes and stories.

A 19th century library favored by Edgar Allan Poe and H.P. Lovecraft, known by locals as "the Ath."

A graffiti Mecca welcoming artists from around the world.

A bit of retro transportation flair preserved in the world's largest department store.

An artist's cute bronze subway sculptures belie his violent artistic past.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.