Starting in 1947, a series of unexplained events and sightings prompts U.S. government officials to become alien hunters; theorists offer evidence that similar endeavors were made thousands of years ago.

Theorists speculate about metal artifacts that could provide physical evidence of extraterrestrials visiting Earth in the distant past; in Jacksonville, Fla. a strange metallic sphere falls from the sky; an ancient aluminum wedge baffles historians.

In the southwest corner of the Wiltshire, England countryside lies the mysterious structure known as Rudloe Manor. On the surface, it appears to be nothing more than a quaint English manor house, but researchers have argued for years that it has been the epicenter of British research into UFOs since World War II. British Ministry of Defence (MOD) insiders claim that an astounding 2.2 million square feet of vast caverns divided into many smaller chambers lie buried underneath Rudloe Manor. Giorgio A. Tsoukalos and Nick Pope explore the possibility that important files related to the history of the UFO phenomenon are being kept under lock and key here. Might recovered extraterrestrial craft be stored and analyzed there as well? Could the evidence of extraterrestrial contact from the Berwyn Mountains incident in 1974 and the Rendlesham forest encounter in 1980 be hidden in this highly protected facility?

Many of the architectural marvels of the ancient world bear striking similarities to one another, even though they were built by civilizations that were separated by thousands of miles and are believed to have had no contact with one another. Separated by more than 7500 miles, the Giza pyramid complex in Giza, Egypt and the Avenue of the Dead in Teotihuacan, Mexico contain pyramids that are aligned with the constellation of Orion's belt. An ancient pyramid temple in Cambodia known as Baksei Chamkrong is an almost identical match for the Temple of the Jaguar in Guatemala. Many structures built using stone slabs that weighed over a hundred tons. But how did primitive people achieve such extraordinary feats? And why do we see such similarities? Could these sites have all been designed by alien architects?

According to legend, a curse was placed on the tomb of King Tutankhamun; researchers theorize that the curse came about as the result of alien technology with the purpose of protecting the truth about an otherworldly event as well as an alien device.

Archaeologists and anthropologists make discoveries that receive no notice because they don't fit into the accepted scientific paradigm, such as an ancient hammer found in Texas or elongated skulls found on nearly every continent.

Researchers suggest that the ancient site of Teotihuacan in central Mexico was once home to a highly advanced, perhaps extraterrestrial, civilization; excavations at Teotihuacan have unearthed discoveries out of place in the ancient world.

The use of mantras and chanting to connect with a higher plane has existed in cultures all over the world dating back thousands of years, but why would people who had no contact with each other all subscribe to this practice? Could there be certain frequencies that connect us with greater - perhaps extraterrestrial - forces? Researchers have found that dozens of megalithic sites stretching across the globe - like the prehistoric Newgrange monument in Ireland, the chiseled labyrinths underneath the island of Malta, and the giant temple complex of Angkor Wat in Cambodia - were all designed to emanate the exact same frequency. The planets in our solar system each give off a distinct sound, and certain places on Earth, like Taos, New Mexico, have been found to produce a hum from an unknown source. Might the best evidence of alien intervention on Earth be found not with our eyes... but with our ears?

A roll of film surfaces containing pictures of a memo informing president-elect Dwight Eisenhower about the existence of a top-secret group of scientists, government officials and military personnel who investigate reports of UFOs.

Researchers ask if Cloud computing represents the rediscovery of an ancient repository of knowledge known as the Akashic Record; neuroscientist Dr. Dario Nardi measures the brainwaves of Dr. Deepak Chopra as he enters a state of deep meditation.

India's Sanskrit texts are filled with incredible stories about advanced technology in the ancient world. Highly complex building techniques, brain surgery, flying crafts, and even nuclear physics are described with uncanny accuracy. Hindu scholars attribute this knowledge to a time when "gods" walked among men. Might this period of time actually be referring to an age when extraterrestrials inhabited the planet? Giorgio A. Tsoukalos travels to India to further explore the Sanskrit texts, as well as the structures and technology that have stood the test of time. From a temple that inexplicably survived a major earthquake to evidence of ancient brain surgery and instructions for advanced flying machines, Giorgio studies the sacred knowledge that is said to have come directly from the voices of the gods.

Extraterrestrials are almost always envisioned as humanoid, but is this an egocentric concept? Could it be that intelligent alien life looks much different from us, and that some extraterrestrials more closely resemble other animals? And is it possible that many of the animals that roam the Earth have otherworldly origins? By examining ancient cultures around the world, we find that nearly all revered certain animals and depicted their gods with animal traits. The Sanskrit epics of India feature gods in the form of elephants, monkeys, and snakes. The Sumerians depicted gods with bird heads and wings. And in Egypt, not only did they portray many of the gods with animal features, but they even went so far as to mummify their animals. Ancient Astronaut theorists suggest that certain animals may not have developed through Darwinian evolution, but were planted here by alien visitors.

While more than 1.5 billion people believe in reincarnation, ancient astronaut theorists suggest that extraterrestrials designed the human body to be a vessel for otherworldly entities.

Japanese legend states that the Ishi-no-Hoden megalith, carved from a single rock and weighing roughly 500 tons, was built to depict a sky ship made of stone that the ancient people witnessed descending from the heavens.

In China, hundreds of strange disks are discovered in a cave that appear to tell the story of an ancient extraterrestrial crash on Earth; shortly thereafter, the disks are confiscated by the Chinese government and dismissed as a hoax.

The ancient site of Gobekli Tepe challenges what archaeologists believe about the past; the megalithic stone complex was built over 12,000 years ago, 5,000 years before the first known civilization was said to have emerged in Mesopotamia.