Cave shrine on Monte Pellegrino.

A network of underground water channels that dates back to the Middle Ages.

Every inch of this chapel is covered in craftsmanship from across the world.

This Arabesque Italian castle was built with a primitive, if ingenious, air-conditioning system.

Haunting graffiti left by prisoners of the Spanish Inquisition.

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

The mastermind behind this palatial hotel perished on the Titanic weeks before its grand opening.

This futuristic airport terminal was abandoned for decades before reopening as a hotel—with a vintage plane of its own parked out back.

A dozen U.S. presidents have stayed at the historic resort, which was known as James Buchanan’s “Summer White House” from 1857-1861.

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

This extraordinary Depression-era expenditure was modeled after a postcard of a Mediterranean hotel.

The legacy of baseball great Roberto Clemente is preserved in a retired Pittsburgh fire station.

North America’s largest collection of horological devices and home to a colossal clock with a dizzying array of features.

The last street in Pittsburgh that's paved with wood.

Long hidden under grime, the politically radical murals of a little known Yugoslavian master are finally getting their due.

Its vintage camera collection gives a snapshot of the past as viewed through a photographic lens.

The residents of the Neighborhood of Make-Believe live without much fanfare within the Pittsburgh Children's Museum.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

Dr Barnes' $25 billion private collection of art and arboretum.

This church in Pittsburgh is home to the largest collection of religious relics in North America.

The house that Frank Lloyd Wright "(shook) out of his sleeve at will" at the age of 86.

In which a local geological marvel becomes a quaint roadside attraction.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.

Once the "Eighth Wonder of the World," this iron railroad bridge was decimated by a tornado.