Amazingly detailed marble cinerary urns that once held the cremains of Roman elite.

The oldest operational cathedral in the U.S. has one shell of a way of projecting speakers' voices.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

This historic Jewish cemetery sits right in the heart of a Detroit car factory.

Cleveland's giant "free" stamp is a nod to the Civil War, but was misinterpreted for years.

The heroic sled dog of the 1925 serum run is preserved in taxidermy.

This Roman statue is missing a limb from when the Venetians stole it from Constantinople during the Crusades.

Knoxville’s architectural icon was the symbol of the 1982 World’s Fair, even catching the googly eye of Bart Simpson.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

An abandoned Byzantine fortress and notorious prison.

A copy of the famous statue can be found in this Florence piazza, along with one of the most breathtaking views of the city below.

Italy's third-largest Roman arena gives a peek into the underground operations beneath the ancient spectacles.

The world’s largest Masonic temple was saved by the White Stripes.

The massive machine creates cracking displays of indoor lightning.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

Two stone columns flank the grand Venice square, but there were supposed to be three.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

Deep in the countryside lie the remains of one of the grandest Roman dwellings in Britain.

The Roman Emperor's lost summer home and grotto full of enormous sculptures sit along the Italian seashore.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

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

The underground sanctuary of a mysterious ancient Roman religious cult contains an exquisite traditional fresco.

The abandoned ruins of America's first private zoo are open for exploration in the Catskills.