A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

One of the most important yet well-hidden museums dedicated to the history of medicine.

Ancient ruins hidden underneath a modern luxury hotel.

Roman-era ships unearthed...

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

Jesus' footprints and the first catacombs in the world.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The notorious "Hanoi Hilton" where Vietnamese colonial subjects and later American POWs, including John McCain, were imprisoned.

These crumbling towers are some of the last remnants of a centuries-old Vietnamese culture.

This striking landscape in northern Vietnam contains both geological and archaeological wonders.

This spectacular bridge supported by two gigantic hands looks like something out of a fantasy universe.

World's largest cave was only discovered in 1991, and now offers tours to the public.

American bombs, morbid memorabilia, and graphic photographs tell the story of the CIA-led “Secret War” from the Pathet Lao perspective.

This impressive clifftop temple was once at the center of an international custody dispute.

This Cambodian riverbed is covered in ancient Hindu carvings both above and below the waters.

One of the most well-preserved temples of ancient Egypt.

Once one of the largest rooms full of books in the world, this bookstore basement is still a treat for bibliophiles.

These flying foxes dangle from the trees around the library like fuzzy black fruit.

Australia's only active volcanoes and highest peak are located on these remote islands thousands of miles away from the mainland.

A little-known museum of Ancient Roman and Ancient Greek artifacts.

An exquisite tunnel of cascading flowers.