The Deepwood is something akin to an anti-Dark Zone, where instead of darkness and futile light sources, there exists a landscape of unsettling beauty and flora. Going deeper into the Mechana Forest warrants entrance to the Deepwood, which holds a certain magic that not even the Mages in Karaten can understand. Humans who travel into the Deepwood are subject to two things happening: either being eaten alive by the arcane energies inside of it, or being turned into one of the phantoms of the Deepwood, a Papilion. The Deepwood isn't something just anyone can enter; the Mechana Forest is warded off to those unlicensed by Karaten, and it is not advised to enter either.
It is likely that the Humans who manage to survive the Deepwood more often than not are Karatynns themselves, but this is not something that has been proven.