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

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

A shining, cold, black organ lies in San Francisco's financial district.

Maryland's first (and last standing) toll house on America's first federal road established the state as the "Gateway to the West."

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

This one-room cabin where the young colonel slept during the French and Indian War.

Faceless white figures loom over the city from the rooftop.

Over 315,000 preserved amphibians and reptiles in jars.

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

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

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

The highest point in Florida is still the lowest high point in the country.

Designed by Maya Lin, the memorial honors 41 individuals who died fighting for equal rights between 1954 and 1968.

Colloquially known as "the lynching memorial," this is the United States' first memorial to the victims of racial terror at home.

This large cave is a summer home to thousands of bats and has a rich history dating back to prehistoric times.

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

An Industrial Revolution-era public work that purified water using nothing but sand.

The span is crooked and made from two older recycled bridges.

Every drop of D.C. tap water flows through this old waterworks.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

These unusual rooms on wheels are holdovers from the 1960s.

This pun was simply waiting to come to life, and one defense contractor made it so.

Built by the patriotic residents of Boonsboro in a single day.

Giant acorn-shaped 19th century gazebo from which suburban Washingtonians gazed upon the original "silver" spring.