The Labyrinthine Worlds are nine planets known to the Hegemony to contain a mysterious complex of underground tunnels. Five of these worlds are within the Web, the rest are in the Outback. Not created by any natural means, the tunnels are hypothesized to have been carved by an ancient race named the Builders by the Hegemony.
All nine labyrinthine worlds share a set of common characteristics:
- Earthlike – at least 7.9 on the Solmev Scale
- In orbit of a G-type star
- Tectonically dead
- Labyrinths typically 10-30 kilometers deep
- Cross-sectional measurements of 30 meters square