The world's most active stratovolcano is almost always erupting.

2300-year-old Roman road connecting the empire.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

This castle was established by the 4th Duke of Montrose and is connected to the Buchanan Clan.

A six-ton wedding present for the King of the Scots.

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

The true age of this ancient stone circle is unknown, but its stunning vista isn't in question.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

Possibly the oldest of Britain's ancient henges is also one of its most stark.

One poet's handmade, anachronistic home.

It's not your typical library, memorial, or book store.

A tree grown from astronaut seeds which were exposed to cosmic rays.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

The restored and active Victorian-era final resting place of San Francisco.

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.

Recovered from the brink of extinction, at home in the Financial District.

San Francisco's newly reopened hands-on science museum.

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

One of the oldest living oak trees in the Southeast.

This grave marks the final resting place of a legendary frontiersman... unless it doesn't.