Nearly as infamous as the Shrike itself, the Tree of Pain, also known as the Final Tree, is a fabled tree of thorns and an integral part of the Shrike legend and folklore as told on Hyperion, being the location of the horrifying thorns upon which the Shrike, like its namesake carnivorous bird, impales its victims (when he chooses not to eviscerate and outright kill them). Countless victims are said to be hanging alive from this quasi-mythical tree, having their bodies pierced and left hanging on the terrible structure by the Lord of Pain. Although apparently a senseless source of cruelty, the Tree of Pain is an important instrument in the Shrike's mission and in humanity's Atonement as understood by certain religious groups such as the Templars and the Church of the Final Atonement.
The Tree was of gigantic proportions - it appeared larger than the valley and taller than the mountains the Seven Pilgrims had crossed on their way to the Time Tombs. Its upper branches seemed to reach into space. The tree was steel and chrome, and its three-meter-long branches were thorns and nettles. Human beings struggled and wriggled on those thorns—thousands and tens of thousands. The sky around it was red in color.
In the event that a Shrike chooses not to kill a victim, it often takes them and impales them on one of these thorns, where they live on in agony for an eternity without the relief of death. The exact location of the tree is unknown to most in the galaxy; it is commonly believed that it resides in the universe's far future or in an alternate dimension.
SPOILER ALERT! The section(s) below are MAJOR SPOILERS.
Martin Silenus was taken by the Shrike as he attempted to finish his Cantos and impaled on the Tree. While being taken there, he realized he recognized some of those forms. He noticed that they were bodies, not souls, and they obviously were suffering the agonies of a pain-filled life.
During the events of The Fall of Hyperion, it is revealed that the tree does not, in fact, actually exist: it is a highly-advanced simulation, with the Tree's victims being unconscious and hooked up to the simulation via neural connectors. This does not diminish their pain, however, and none within the simulation suspect that they are not suffering the physical torment of impalement. The victims of the tree are physically located within the Shrike Palace, although they are not normally visible because they are out-of-sync with the observer's present.
The Shrike's goal during the Web Era was to locate the host of the human Ultimate Intelligence that existed in the far future. Due to the horrific nature of the conflict between the Human UI and the TechnoCore UI during this period in the future, the human UI sent a fragment of itself into the past, containing the components of itself capable of empathy. This fragment would then take residence in the consciousness of a human individual. The Tree of Pain was designed to broadcast sensations of pain into the Void Which Binds, thereby attracting the attention of the fragment and drawing it into the open. The identity, nature, and mission of the human host to the Human UI fragment are revealed and brought to their conclusion in the last two novels of the saga, Endymion and The Rise of Endymion.
- The Fall of Hyperion, 1995, Ch. 21