You have a map of about a mile into the caves; there are areas you have not explored yet. There is lichen, various other underground plants and fungi, fish, insects, some weasels and foxes, and a few of the more 'magical' beasts (the predators) - it's really not a great environment for animal life to flourish in.
As far as you've explored, the river starts somewhere out of sight on the prairie (you've only gone to the forest's northern edge where the prairie begns), through the forest, then down into "your" cave after flowing over the waterfall, though it does branch off a couple times both above and below ground. A couple of the aboveground branches go into smaller caves. The river keeps going for miles underground, but you don't know where it ultimately ends up.
Cepter - sorry, but I'm going to keep it at five for now. It's already taking a lot more time and way more effort than I was originally prepared for. I'll certainly put you on the alternate list after Kalanyr, though.
John - Sorry; I'll edit.