When first discovered, the planet seemed to be a fairly standard Arean type world. Seismic surveys discovered otherwise. First discovered at the North pole of the world and found to extend under its entire surface was a huge, apparently artificial, complex of tunnels and chambers, some of them nearly a kilometer across. As quickly as possible, an expedition was outfitted and a passage was drilled into the tunnel complex.
What the researchers found was astonishing. The entire tunnel complex is home to an underground ecology of great complexity. Totally adapted to the lightless existence of the caves, life forms rely on hearing, smell, touch, thermal perception and natural sonar to navigate a world without a sun.
Numerous artificial geothermal vents provide both heat and atmospheric gases which are processed by a complex of fungus and moss like plant forms into a breathable atmosphere. Deep wells and underground rivers, lakes and even small seas provide water. Life forms ranging in size from bacteria to larger than an elephant live in the cave complexes although no sapient life forms have ever been found.
A view inside the caves of Labyrinth, showing a colony of stalactite-like dangleworms
The Labyrinth complex is believed to have been constructed some 10.7 million years ago by an unknown alien race. While archaeological studies have found the remains of machines which are believed to have been used to construct the tunnel complex, no other artifacts have been found. The purpose of the tunnel network whether habitat, experiment or artwork is unknown.