Hollow Earth Tunnels

The Hollow Earth Tunnels, or HET for short, as explained in previous pages, is a global subterranean ecosystem formed from interconnecting caves, of which are mostly solutional (formed by acidic groundwater streams). 

This realm is notable for its evolutionary history as it houses dozens of ancient lineages from as early as the Mesozoic, and for giving rise to sunlight-independent radiotrophic plants which - along with bioluminescent fungi - can form truly spectacular glowing forests. 

However, very little of this realm is fully understood. It is currently unclear the impact exploring this totally isolated ecosystem would have. Additionally, some of the native wildlife pose a profound threat to explorers and anything else for that matter. For now, exploration is heavily limited and managed with a fashion similar to that of Antarctica.