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; today, it lies in ruins, but some researchers believe these stone blocks hold profound secrets about an extraterrestrial civilization that existed in ancient Egypt long before our recorded history.

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. Could it be that these islands are the remnants of a lost alien civilization?

Host Giorgio Tsoukalos probes the series archives to explore remarkable ancient structures that defy conventional explanation. 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. Might the secrets of the Vedas reveal the truth about extraterrestrial contact in the distant past?

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?

Host Giorgio Tsoukalos probes the series archives to present the most compelling UFO SIGHTINGS. From footage of extraordinary aircraft taken by fighter pilots to a strange object filmed flying over a military base in Iraq and 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?

Host Giorgio Tsoukalos examines series archives to investigate theories of historical extraterrestrial contact; the broadcast reviews aerial geoglyphs, crop circles and mathematical codes embedded in ancient global architecture to assess claims of early astronomical communication.

A documentary examines how researchers utilize remote-sensing technology, such as lidar, to map previously undocumented ancient urban networks beneath the Amazon canopy; the broadcast investigates alternative history theories regarding potential extraterrestrial influence at these newly mapped archaeological sites, evaluating whether the design of these pre-Columbian settlements aligns with ancient astronomical patterns or cosmic structures.

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.