"It's a fungus. It uses the body the way a mushroom grows on a rotting log. Eventually, when the body breaks down too far to use anymore, it just lets the body drop and it sends off spores. Little bits of itself on the air, hoping some person will walk through and breathe it in."

And there's a little spot that looks like it might be the way back down off the other side, like the map showed. Tess heads off down the incline.