It's just after the ending, but before the credits, I just checked.
Then it gives you a clue what to do to get into the other path.
"Congratulations on your excellent performance! If you want to go "beyond" the ultimate score, we recommend that you try the other, "easier" entrance to the castle. You can do so easily by restoring back to a point just before the Druid's rain storm. DON'T GO BACK TO SEE THE DRUIDS--instead, head to the castle. New puzzle challenges await you!"