Open Everything:
When you meet the old priest with the funny green hat (he's usually outside his hut), offer him one of your magic spells. When he chooses the spell he wants then cast that spell. During the spell casting animation press Esc and you will bypass the animation. This makes the old man ask "Where's the spell son?" Now choose the 'Help" response. This will make the old man go back into his hut. When he returns he will give you one of the hidden secrets. Repeat this until you have unlocked all the secrets. There are 20 in all.