its to the south-west of the man IIRC. You have to find a little way in between the mountains. You'll know if you encounter a place with butterflies and the char sneezes(IIRC). The cave is overthere. But watch out he isnt that easy.
If you cant find it, check this link for a complete map of the dark forest(made by Dragon).
http://free-ri.hinet.hr/dragon/dark_forest_locations.jpg 
