This historic California cemetery holds the bodies of veterans of both the Civil War and the Donner Party.

California's own majestic geyser is powered by a subterranean volcano.

California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

The fossilized remains of ancient California redwoods.

This icon of the Atomic Age now lays dormant.

New York City's smallest piece of private property.

Forget Hollywood, one of the biggest stars in the world can be found in Roanoke, Virginia.

Giant busts of 42 U.S. presidents are sitting in a field in Virginia.

This maze-like slot canyon is a unique gem within an already fascinating geological area.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

Big gun installations, built over a massive cemetery, now abandoned & hidden in trees.

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

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

This mysterious series of teeny guerrilla installations sheds a whimsical light on street art in Oakland.

Collective dedicated to restoring steam engines.

A restored 1920s cascade stairway provides one of the best views of Oakland's Lake Merritt.

Pensacola's UFO home has withstood many hurricanes—just as the experimental 1960s design intended.

One of the only Florida forts to remain in the hands of the Union all through the Civil War still stands as a historic stronghold.

This now-deactivated naval base defended the Florida coast for centuries.

Rowdy rebels fortified this home during the first popular uprising in United States history.

This museum explores the grim reality of life in the earliest British colonies in America.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

This popular Boston haunt is reminiscent of a time gone by, when slow cafes and sweet-smelling smoke wafting from patios was the norm.

A dollhouse full of taxidermy rodents, each one handcrafted and given a sordid past.