In every corner of the world, archaeologists have found strange, elongated skulls. Did our ancestors modify the shape of their skulls to resemble extraterrestrials? And might it even be possible that some of these skulls are of otherworldly origin?

High above the Giza Plateau stands Egypt's most mysterious ancient site: the Lost Pyramid of Abu Rawash.

In the western Pacific Ocean is a vast area known as Oceania that is home to the world's most remote and mysterious islands. They are known for massive stone structures, statuary strange figures, and countless legends of otherworldly visitors.

From the precisely cut stone blocks at Puma Punku, to the gigantic temples of Malta, and the megalithic city of Nan Madol, could these mysterious sites contain evidence of extraterrestrial contact in the distant past?

Found along the California coast to New York's Hudson Valley, and Northern England to Southern Chile, could these mysterious locations provide evidence of an extraterrestrial presence on Earth?

From a stone circle in Turkey that challenges the timeline of human history to gigantic stone spheres in Bosnia and Egypt's most unusual tombs, could these monuments provide proof of extraterrestrial visitation?

The oceans are the most mysterious places on Earth. Countless legends tell of powerful beings living in the waters, and today they are major hotspots for UFOs. Is it possible that the deepest depths of our planet-are home to otherworldly beings?

Ancient scriptures called the Vedas form the foundation of Hinduism. These manuscripts are thousands of years old and describe a time when Earth was inhabited by gods who traveled the skies in flying machines and possessed extraordinary technology.

Ancient legends describe a war in heaven that was fought by otherworldly beings with extraordinary weapons. Is it possible that our planet still bears the scars of battles fought by extraterrestrials?

From footage of extraordinary aircraft taken by fighter pilots to mysterious glowing orbs that are reported all over the world, are these remarkable sightings evidence of extraterrestrial visitation?

The rapid development of artificial intelligence has made it a powerful tool for historians and archaeologists. But might it also reveal evidence of an extraterrestrial presence on Earth?

From colossal figures that can only be seen from the sky to complex crop circles that mimic sound frequencies, and mathematical messages encoded on opposite sides of the planet, could these sites hold clues about alien visitation?

The Amazon rainforest remains largely unexplored, but thanks to new technology, researchers are now finding that this dense jungle was once home to a vast network of cities.

Host Giorgio Tsoukalos opens the series archives to celebrate ALIEN INVESTIGATORS that have been brave enough to ask the question, Are we alone in the universe? Could these investigators have uncovered proof of an alien presence on earth?

The origins of humanity can be traced back to Africa, and some of the oldest religious traditions across the continent describe mysterious beings who descended from the sky in thunderous vehicles.