Mark Twain National Forest, haunted by hellhounds and other demonic creatures, may also conceal treasures from a lost civilization, pointing to the area's importance as a locus of dark, mysterious energies.

A bizarre series of incidents in Big Bend National Park suggests that extraterrestrials are present in this remote wilderness area, leading experts to conclude that aliens have been secretly mining rare minerals there for years.

The shimmering waters of Crater Lake National Park captivate visitors, but they may also be the epicenter of dark, sinister forces from Native American lore that lure visitors to their deaths, conceal a terrifying monster and produce ghostly apparitions.

Mysterious lights, mechanical sounds from deep within the Earth and the disappearance of dozens of aircraft over the Great Smoky Mountains National Park could be evidence of a powerful secret society with an underground base in the area.

An alien abduction and strange encounters with a humanoid monster in Apache-Sitgreaves National Forests point to a longtime extraterrestrial presence in the area. Are aliens using the forests to monitor nearby nuclear weapons facilities?

A series of disturbing deaths and disappearances, plus the unearthing of artifacts from an ancient race of people in Death Valley National Park leads to the discovery of malevolent forces that are believed to inhabit the park's secret underworld.

A demonic truck driver, disembodied voices, nightmarish skinwalkers and a time loop are among the bizarre phenomena found in Canyonlands National Park, where the mineral quartz may be acting as a recorder of human experience.

Black magic, mysterious deaths, and violent fireballs haunt Hawaii's Volcanoes National Park. Many believe this is the work of Pele, the fire goddess.

A Bigfoot-like creature and UFO sightings suggest that California's Joshua Tree National Park may be ground zero for alien genetic experiments.

Ghost sightings, a secret government time-travel experiment, and Native American battles suggest that Pennsylvania's Gettysburg National Military Park is a place of unusual and mysterious power.

Ghosts from a bizarre plane crash and a mysterious underground city point to powerful forces at work inside the Grand Canyon National Park.

Unexplained disappearances, a mysterious death and a Karuk Indian legend may be linked to a race of superhumans in California's Mount Shasta National Forest.