Since the 1700s, this old barrel has acted as a post box that relies on the kindness of travelers.

An artsy hidden staircase leads to breathtaking views of San Francisco.

These pretty kitties killed and ate as many as 135 railway workers.

Sniff the Titan Arum's rotting flesh.

The land is home to swimming ponies and a legendary 18th-century treasure.

A museum dedicated to exhibiting remarkable outsider art.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

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

The longest continuous lava tube in Oregon.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

A self-built castle made by a mysterious man.

Op-art architecture designed for happiness.

A giant Troll lurks under one of Seattle's oldest bridges.

A marvel of Byzantine engineering under the streets of Istanbul.

This famous city eluded concrete detection until the early 2000's.

This historic "City of the Dead" lies prominently in the center of New Orleans' famous Garden District.

This historic Victorian hotel has a scandalous history of affairs and murder.

Four, 18-foot-tall badminton shuttlecocks lie scattered about the lawn of a Kansas City museum.

Only hotel where you can legally launder money.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

Golden Gate Park's historic collection of plants.

The remains of a 12th-century chapter house in Golden Gate Park.