A replica of one of the more than 15,000 civilian lookout towers that lined the U.S. coast during World War II.

Inside an old airplane hangar, friends and strangers alike play on a massive trampoline.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

Austin’s nonprofit-run graffiti park where street art is meant to be painted over.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

The largest earthwork effigy in the world.

A failed utopian experiment for British expats in the American South is now a Victorian village frozen in time.

Mile-long cave system near Great Smoky Mountains.

This replica of the Greek structure is in the heart of Nashville.

An image of the legendary saint stands in the shadow of a cathedral she liberated.

Peeing dogs guard the Roman hunting goddess atop a fountain at France’s Château de Fontainebleau.

César Baldaccini's iconic sculpture of a 40-foot thumb stands tall in La Défense.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

This stunning French estate was so lavish that it landed its original owner in jail for the rest of his life.

The famous winding walk at Chartres is surrounded in mystery and myth.

This skewed English house has looked like it's going to fall over for centuries.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Eighty million natural history specimens call this gargantuan museum home.

Hear the quietest sound from across the dome.

A medieval replica of King Arthur's legendary table, the Round Table hanging in Winchester Castle was decorated by Henry VIII.

This ruined medieval castle was the scene of Lord Robert Dudley’s seductive reception for Queen Elizabeth I.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.