High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

A multi-storied adobe complex has been inhabited for more than a thousand years.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.

Legends surround this jagged rock formation in the New Mexico desert.

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

This ruined fort hidden at the top of Central Park can't seem to keep from losing its historical plaques.

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

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Quite simply the largest tree in the world (by volume).

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The magic's in the hole!

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

A beautiful geyser under environmental threat.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

The first declared National Monument in the United States.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

A walk through the historic city center, under the streets of Seattle.

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

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