Sections of the iconic limestone columns have been left uncleaned as a reminder of the city's polluted past.

The largest clock face in the United States is twice the size of Big Ben and infinitely more ad-sponsored.

The United States’s oldest funicular railway glides up and down a steep Pittsburgh street.

The last remnants of Fort Pitt also hold the distinction of being the oldest structure west of the Allegheny Mountains.

Meet your friends, marry your true love, or tell your enemies to kiss your butt under this historic Pittsburgh timepiece.

This historic graveyard was partially paved over to create a streetcar line.

San Diego's most historic and haunted home.

Crispy, cheesy rice balls—the Roman answer to arancini—take center stage here.

This subterranean shrine beneath a bike rental store celebrates the iconic Italian scooter.

Inside this McDonald's you can dine on your Big Mac and fries next to a 2,500-year-old Roman wall.

For more than a century, this hole-in-the-wall near Termini Station has been serving what some say is the greatest porchetta sandwich.

A sculpture serving as an homage to Pope John Paul II.

Its interior is adorned with some of the best examples of early Christian mosaics.

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

An alchemist's “magic door” stands in the middle of a Roman park.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

This small pedestal marks the spot of the first lot of land sold in Alexandria, Virginia in 1749.

The romance of early commercial flight still fills this Art Deco destination.

Water and windows define this defensive Italian well.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

An enigmatic modern marker left next to a historic Roman site.

Nicknamed “The Mushroom,” this unique water tower has been featured in several iconic movie scenes.