Coway shafts were underground tunnels used by the Coway to travel beneath the surface of Mimban. They were well-lit with phosphorescent growths. The Coway would often connect these tunnels to existing Thrella wells for surface access. They did not bother to hide their egresses to the surface. The Coway shafts could be quite extensive, including underground rivers and lakes, and large chambers that could house entire tribes of Coway numbering in the hundreds.