A neighborhood church's unusual abstract stained glass was the final project of avant-garde artist Jean Cocteau.

Visit Europe's largest subterranean waterfall, carved by water from the glaciers of the towering peaks surrounding the valley.

Liechtenstein's royal family calls this medieval alpine castle home.

The smaller of the three towers of San Marino is a former prison inaccessible from the ground level.

One of the largest squares in Europe contains an entire artificial island.

This amazing medieval fortress stands atop a promontory along the famous Cinque Terre.

The world's most active stratovolcano is almost always erupting.

A rare underwater observatory in the Caribbean that provides breathtaking views of vibrantly colored aquatic life.

The first location of the eventual video game giant.

Its columns were all carved from the same white oak tree.

The highest point in New Jersey is marked by a massive, if simply named, obelisk.

World War II-era bunkers are hidden under the beaches of this picturesque park, which is still scattered with wartime watchtowers.

The stone marker that Mason and Dixon placed at the eastern end of the famous north-south border they surveyed.

This field of concrete was once an active defense site armed with nuclear warheads.

This unique structure is the only one of its kind in Virginia.

This Virginia railway overpass is said to be haunted by a serial killer in a rabbit costume.

A 14-foot monument marks the resting place of two of the town's earliest residents—and one unknown soldier.

Parking garage where Bob Woodward met Watergate source "Deep Throat."

A gift from Japan, 17th-century lantern stands among the cherry trees at D.C.'s Tidal Basin.

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

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

Holy Grotto of Montserrat Monastery holds one of Europe's mysterious black Madonnas.