This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

An elaborate gift from Claus Spreckels is now a piece of San Francisco history.

Golden Gate Park's historic collection of plants.

One of few lasting examples of the brief octagon craze that developed into folly.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

San Francisco's oldest surviving monument and meeting place for 1906 survivors.

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

Visible below the waves are memorials to the city's Gold Rush dead.

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

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

A winding path built in secret on the edge of the continent.

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

The once highest point in China blends symbolic design with a kick of adrenaline.

This psychedelic tourist trap is a leisurely descent into madness.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

The most famous location in China was home to whole dynasties worth of imperial rulers.

This historic hotel invented the chocolate brownie.

This bronze sculpture on a former squash court marks the secret origins of the Atomic Age.

The unluckiest U-boat in the entire German fleet is now on display in a Chicago museum.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.