If I remember correctly there was a network of underground rivers throughout shing jea island, how extensive was this network? is there a similar network spread throughout the mainland of cantha also?
Underground rivers are not wholly uncommon. There are aquifers all over our world, I think it would stand to reason the Tyria is similar.
The wiki page on aquifers is pretty interesting if you are curious about underground water supplies.
Lead Game Designer with a primary focus on Living World content/story