The oldest continuously operating fish market in the United States.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

The site of the climactic scene from the classic horror film is now a historic landmark.

The United States Capitol's former columns still stand.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

This failed condo development was reborn as a street art hub.

A 131-year-old wunderkammer of Texas history.

Three hundred years of preserved Spanish colonial history in San Antonio.

A master plumber has turned his love of art and toilets into a folk museum that's not taking the piss.

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

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

A collection of 20th-century automata, penny arcade games, and musical contraptions.

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.

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

A plaque commemorates the spot in the Oregon woods where the first-ever Geocache was hidden.

This outpost of America's most popular fast-food restaurant is housed inside a palatial mansion.

The former estate of the Guggenheims, part of the opulent Gold Coast that inspired the Great Gatsby.