The Forbidden Jungle is just that, a jungle. The perimeter and surrounding areas have been thouroghly explored, and have been mapped up to ten miles into the dense growth. But the interior remains a dark mystery.
It is well known that the Forbidden Jungle is infested with dangerous creatures, including amphibious pirahnas, carnivorous locusts, venomous birds, hostile and mobile plants, flying snakes, and frighteningly intelligent predators. And those are just the documented species. There are also the things you would normally expect, such as regular (and highly poisonous) snakes, lizards, and frogs, crocodilians, stinging and biting insects, and poisonous plants. There are rumors of people living deep within the jungle, but no one who’s ever gotten that far has ever come back. People have found what appear to be territorial markings in the jungle. But no one really knows for sure.
The Jungle is a place where something seems to have gone horribly wrong, and nature has decided to eliminate people with extreme predjudice. Sometimes, those who dare venture into the dark unknown of the jungle return with hideous deformities. Sometimes they go in with hideous deformities, and return without them. Of course, many do not return at all. No one really knows what happens in the jungle once you are beyond the immediate reach of civilization.