The world's longest known cave system.

The largest earthwork effigy in the world.

This legendary urban waterfall creates a dazzling display of rainbows.

This black shoreline is made up of exploded lava particles.

Earth's tallest volcano is sacred to Native Hawaiians, and home to a dozen world-class observatories.

Hide from the tourist hordes in these relatively unknown, and unguarded lava caves.

These picturesque Hawaiian falls are home to a rare species of fish that uses a special sucker to climb up cliffs.

The southernmost point in the United States is a beautiful place to look at but a deadly place to wade in.

A beach made of semi-precious green sand on the Big Island of Hawaiʻi.

In 2018, Pohoiki Road was severed by lava flowing from the eruption of Kilauea.

This war hero's old shop remembers the fine line between medicine and quackery during the Revolutionary War.

The scene of one of the darkest moments in American labor history has been left essentially untouched since the tragedy.

Once a lonely sentinel on the edge of the Great Plains, this rebuilt trading fort offers a glimpse of life on the Santa Fe Trail.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

Turning night into day in Victorian-era Austin to thwart a serial killer.

Locals dubbed it the "Owl Building" because of its bird-like appearance.

Home to an endangered salamander, a full moon celebration, and a large spring-fed outdoor swimming pool.

One of the longest water bridges in the world was built over a supposedly haunted swamp in Louisiana.

The world-record holder for the longest bridge stretching continuously over water.

A 19th-century shrine covered with prosthetic body parts as votive offerings.

By day this New Orleans square is for pedestrians, but by night it is a kingdom of kittens.

This macabre shop, filled with art, oddities, and taxidermy is hidden in the heart of the French Quarter.

This cathedral dedicated to Louis IX, sainted King of France, holds many secrets.

The oldest operational cathedral in the U.S. has one shell of a way of projecting speakers' voices.