The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

Largest necropolis in the Mediterranean.

The ruins of this Roman temple dominate the small city in southern Lazio.

A research lab and hands-on museum where visitors can experiment with retro technology.

Unlike most arches, this geological oddity formed in a volcanic dike.

One of the largest Buddhist stupas in North America is built of concrete designed to last 1,000 years.

This interpretive path lets you get up close and personal with dinosaur bones.

The largest source of fossilized insects anywhere.

At the tallest peak in Colorado, an electrifying mix of thin air, lightning, and rivalry.

This tea house was a hand-built gift from Boulder's sister city in Tajikstan.

Rather than a run-of-the-mill franchise hotel, this lodging has been decked out in dinosaur decor.

The highest bridge in America was built for an almost unnervingly small amount of money.

The largest self-built castle in the U.S., six decades in the making.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

Paranormal experiences in this hotel's room 217 led Stephen King to write "The Shining."

A wunderkammer of curious objects and intriguing art nestled within a hub of ancient Roman sites.

Legend has it that this bronze orb, which sat atop an ancient Egyptian obelisk, once held the ashes of Julius Caesar.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

Romans decided this 16th-century "talking statue" was so ugly, they named it after a primate.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

A burial vault located under Tiber Island in the middle of the Italian capital.

Roman-era ships unearthed...

This hydrochronometer was invented by a Dominican monk and is a prime feature in this garden.