La Theine Plateau
The route from San d'Oria to Jeuno is probably the most difficult of the three. Before leaving La Theine Plateau, check the Crag of Holla in the center of the map for a crystal that'll let you teleport back here at a later date. From there, head east to the Jugner Forest exit.
While there is a road leading through Jugner Forest, it can be pretty dangerous. The Tigers, Goblins and Orcish will all attack on sight, while the Walking Trees will attack sounds. Follow the road northeast until you reach Batallia Downs.
Once in Batallia Downs, you'll want to head directly east. Avoiding attacks is pretty easy here, thanks to the barrows and hilly terrain, but still be on the lookout for Tigers, Goblins and Orcish, all of which attack on sight.