Could the darkest recesses of our planet contain important information left by our ancient ancestors? And within Earth's mysterious caves, might we find evidence of otherworldly contact?

The Great Sphinx in Giza is the largest and most studied monolithic sculpture on Earth, yet it remains one of humanity's greatest mysteries. Who-or what-created the ancient monolith?

Could it be that our increased reliance on computers, cell phones, tablets and the internet is the product of extraterrestrial design?

Throughout history, many of the world's greatest thinkers have helped push civilization forward. But is it possible that their genius is more than just good genetics?

For thousands of years, people have practiced techniques to preserve the body after death. Could our ancestors have witnessed a form of extraterrestrial hibernation and mimicked it with mummification?

From Jesus and Elijah to mummies and zombies, cultures around the world are filled with accounts of beings who are able to lift the veil between life and death. Could some of these stories be true?

There are those who believe that embedded in our most sacred religious texts, as well as in the design and location of ancient monuments, are secret messages. Could this be true?

Do the numerous myths and stories of an ancient flood sent by the gods point to an actual deluge? And if so, could aliens have been involved?

The Civil War nearly destroyed the great experiment known as the United States of America, but is it possible that the preservation of the republic was influenced by extraterrestrial beings?

With new technology detecting pyramids hidden underground around the world, many believe we have entered a new pyramid era-an age of discovery that will be marked by unimaginable findings.

Stories of civilizations large and small disappearing without a trace can be found throughout history and across the globe. Could extraterrestrial intervention be behind these vanishings?

Have extraterrestrials been monitoring human progress for thousands of years-at times helping us to advance, and at other times holding us back?

Did our ancestors have an understanding of how to generate power thousands of years before modern man?

Giorgio Tsoukalos decodes some of the most compelling evidence for Ancient Astronaut theory found in mysterious carvings, symbols, and structures that are strikingly similar on opposite ends of the Earth.