The Yggdrasill was a state-of-the-art, beautiful treeship built and designed by the Templars commanded by True Voice of the Tree Het Masteen. It was about one kilometer long. The treeship took the Seven Pilgrims to the Final Shrike Pilgrimage in Hyperion.
The first tale of the pilgrims, the Priest's Tale, of Father Lenar Hoyt, was told in the dining room of the treeship.
During the attacks upon the Hegemony of Man that led to the The Fall, the Yggdrasill was destroyed while in orbit around Hyperion. Het Masteen would later say that it was sacrificed purposefully, offered as atonement for the sins against the Muir.