The remains of an ancient Roman city are hidden underneath Bologna's beautiful public library.

Legend has it this fountain built to symbolize the Pope’s power hides a strange secret concerning Neptune's manliness.

In the world's oldest university is a stunning 17th century anatomical theater carved from spruce.

Ancient ruins hidden underneath a modern luxury hotel.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

Thousands of well-dressed mummies below a monastery.

A "gravitational anomaly" located in the redwood forests just outside of Santa Cruz, California.

A giant Troll lurks under one of Seattle's oldest bridges.

A winding path built in secret on the edge of the continent.

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

Look closely and you’ll notice that the color changes a third of the way up the tower.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

An overlooked memorial honoring the local Washington residents who died in World War I.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.