The Hyperion Cantos (Dan Simmons, 1989)

Hyperion is a linked series of stories, all relating to the mysterious planet Hyperion. The stories are told by 7 pilgrims, while in transit to the Time Tombs of Hyperion, which are opening for the first time in centuries, and are normally inaccessible due to the lethal actions of its guardian, The Shrike. The stories are told against a space opera backdrop in which humankind has formed the Hegemony, a far-flung collective of planetary systems linked by farcaster portals, threatened with attack by the Ousters (who are space-evolved humans) as the novel opens. The novel has elements of both science fiction and horror, and covers a wide range of themes such as: time-travel, artificial intelligence, virtual reality, religion, ecology, and the works of John Keats.