While it's probably more effective to farm wounds directly, if you do happen to have nightmares build up that you need to get rid of anyway then go to the Somnolent Hyena in the Labyrinth of Tigers and gawp until you're down to manageable levels. Even if you fail the only consequence is that nightmares drop by 1 CP and wounds increase by 2 CP, so no matter what you'll trade a little nightmare for wounds.