This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

Steepest flood safety railway in the entire world.

This dramatic rail curve was once the target of a failed Nazi attack.

The remains of a community that was forced to move for a dam that never materialized still rot in this Pennsylvania park.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

The only way to see Pittsburgh is from the top of this lookout point, just like the ancient members of the native peoples did.

The oldest farmer's market in America is so ancient it was approved by the King of England.

The world's tallest doric column is this Ohio monument to a naval victory in the War of 1812.

A historic freight system that found the true gold rush is in tourism.

Curious cave that stays a cool 56 degrees all year long.

European castle ruins in an American state park are actually the product of death and grief.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

This beautiful, historic church looks like something out of a simpler past.

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

The first car-centric shopping plaza in the U.S. brought a little bit of Spain to downtown Kansas City.

The rusting remains are visible sticking out of the waters of the Delaware Bay.

Send a postcard while vacationing with Satan.

This strange bovine gargoyle is said to have been put in as a passive aggressive form of revenge.

A historic house in St. Louis was plagued by a series of suicides committed by family members involved in a successful brewery.

Erosion and time have created a naturally-formed water park.

Huge masonic hall in Philadelphia with lavishly themed rooms.

World War II bunker still standing on the New Jersey beach.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.