The Ark is a transportation device created by an unknown, highly advanced ancient civilization. It is tall and rectangular, made of brownish stone, and smaller at the top than the bottom. It has mysterious writing around its sides and four retractable stone wings on the top half, with a bird head on top where the controls are also located.
It was initially found by Kat lying dormant in Boutoume where Raven was searching without success for a way to enter it. After Kat has her mind awakened by Cyanea, she is able to find the invisible entrance and load the children onto it to bring them back to Hekseville.
It has many strange and unexplained powers, like the ability to travel through dimensions and put the people inside into stasis, in fact, its very entrance appears to be split from the dimension it exists in.
It may have been a device created to escape The Darkness, allowing the ancient civilization to reach the top of the World Pillar and create Eto. This is corroborated by the heavy similarity of Eto technology, with similar stone construction and control methods.
It is shown in the Ark of Time DLC that the Ark is powered by the sealed spirits of Light and Darkness, and tampering with it incorrectly has the potential to massively damage the entire universe. Dr. Brahman's attempt to reverse the stasis of the Ark caused, in the words of Creator Bit, a "system crash" of the universe that resulted in Hekseville freezing up completely and the Collectors attempting to wipe it out of existence.