A labyrinth was a means of space-time travel.
They were networks of open-ended space-time events, allowing transit between the connected points. Considered a "vulgar" form of time travel, they pre-dated the timeships of the Great Houses. It was speculated that they were created by the Eremites. (PROSE: The Book of the War)
The Great Houses' records library was located in a labyrinth buried in the framework of the Spiral Politic. The library was guarded by a sentient extension of the labyrinth resembling the Minotaur, known as Mr Smith. Most Great Houses installations were linked to this labyrinth, including their prison planet. (AUDIO: A Labyrinth of Histories)
During the War in Heaven, labyrinths were used for communication by the Houses, the Celestis and even the enemy. Sometimes truces were declared when rival groups met, since they were afraid of what else might be living in the maze. However, since they could not be secured, labyrinths eventually fell out of use except by Faction Paradox. They would use them to keep in contact with distant Remote colonies, and some claimed at least one intersected the Eleven-Day Empire.