Berlin's old airport.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

This beautiful architectural gem was the first waste treatment facility in Boston.

What was once one of the country's largest confectionary plants is now an abandoned ruin, but is still pretty sweet.

These chunky stone towers out in Lake Michigan are the key to Chicago’s drinking water.

This memorial plaque remembers a strangely shallow maritime disaster known as "Chicago's Titanic."

This modest post office sits on the site of H.H. Holmes' famous murder castle.

A shining sculpture made of 3,115 lights, the number of visible stars in the Northern Hemisphere.

A European-style bath house in Chicago.

What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

The site of the first couple's first kiss is commemorated by the most adorable presidential monument ever.

A speakeasy takes on Chicago's drinking culture.

A rococo retro-futurist future-rustic vernacular between yesterday’s tomorrow and the future that never was.

This eatery transports diners to a place that no longer exists: East Germany.

San Francisco's first World's Fair, dedicated to the wonders of California.

Forgotten and then destroyed by fire, this was once one of the largest saltwater swimming pools in the world.

The only visible piece of San Francisco's most famous shipwreck.

Recovered from the brink of extinction, at home in the Financial District.

This partially buried wreck is one of the most complete of its kind but is only revealed when the sea allows.

A 300-ship graveyard, with a few still visible at low tide.

A modern mechanical planetary system, part of a 10,000 year clock.

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.