This private residence was the template for one of the most beloved television homes of all time.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

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

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

An essential stop before plundering, BYO Cutlass.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

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

San Francisco's newly reopened hands-on science museum.

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

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

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

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

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

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

The most accurate timepiece in the world.

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

Proto-CIA agents trained with grenades in the sand traps and fired machine guns from the fairways.

A double agent hid information for the Soviet Union beneath this bridge for more than 20 years.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.