The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

This cemetery features modernist statues as strange as its name.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

It was once the base for a series of domestic terror attacks.

When it opened during the final years of the embargo, all the drinks and cigars were free.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

The most decorated dog of World War I is preserved in the Smithsonian.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

Alexander Milliner, a favorite of General Washington, is interred at Mt. Hope Cemetery along with 80 other Revolutionary War veterans.

This block in downtown Brooklyn was a hotbed of antislavery activism along the Underground Railroad.

The site of William McKinley's tragic assassination is only marked by an underwhelming boulder.

This city park was once a lookout point for George Washington’s army during the Battle of Brooklyn in 1776.

The first American home of the isolated, egalitarian religion has a trove of Shaker architecture and artifacts.

The mass grave of a heroic Revolutionary War regiment sits below an empty lot near the Gowanus Canal.

Manhattan's Thirteenth Avenue was made on landfill then deliberately destroyed — apart from one small, obscure block.

HBO series' stage tucked away in a Greenpoint lot is the largest theatrical set of its kind in the United States.

Some of the earliest burial grounds of New York State are to be found hidden away in this quaint town.

Where now stands a 42-story condominium tower of marble, glass and steel was once the central market of New York’s slave trade.

Secluded amid upstate New York’s Adirondack Mountains lies this subterranean emblem of a nation on the brink of nuclear war. And it's for sale.

The artist and New York City icon lived, worked and died in this converted carriage house owned by another iconic artist, Andy Warhol.