You must visit every location in the world, including all the hidden forest dwellers and the conductor (available only in a completed game file) for this trophy to fire.
After sleeping in an inn for the first time, hidden locations in the area will be marked on your regional map in the Wizard's Companion. Draw/forage locations will be marked with keyholes; secret forest locations will be marked with mushrooms. Cave locations will be marked with purple cave openings. Be sure to stay at the inn everywhere you visit so that your maps will be complete.