One New Hampshire alleyway has become home to a public gallery of feline art.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

At 207 feet, one of the world's longest continuous escalators.

All that remains of this Massachusetts town, demolished in the name of progress, is a stone marker.

Over 50 whirling pools left behind from the glacial age.

America's post-nuclear-attack chambers of Congress.

The world's longest known cave system.

An abandoned cemetery lies in ruins as the surrounding forest swallows it whole.

A rare view of a preserved Victorian science museum.

Collection of antique science instruments displayed in recreated 1870-1930 laboratories.

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

Ruins of a once-prized railroad station in New York.

Ancient snack bar of the Roman Empire re-opened.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

This beautifully deceptive waterfall is something far different from what it appears to be.

A lake at the bottom of the ocean.

An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.

The meteor that sealed the fate of the dinosaurs landed at this site, one of the largest impact craters in the world.

Astronomical observatory above Lake Titicaca.

Light still pours into the ruins of this ancient Islamic observatory.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.