Here is the full list of all 5 Secret Of Magia achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
You used a nun's magical powers to restore all of your health.
You have arrived at the Mystic Mountains, a terrifyingly mystical place.
You found the strange key to unlock a strange world.
You stayed at an inn and healed your party.
You found the well where you discover your powers.