Shiness: The Lightning Kingdom

This quest can be found in the hidden "Secret Rift" dungeon, which is found behind a hidden Rosalya door in the Forest of Meonis (see "Another World"). Once you enter the dungeon, you will fight a lvl 50 boss (which is from a top-down view like a shmup - use projectile magic only), and then you will need to find a woman to complete the quest. From the entrance of the dungeon, take the left path. Once you return to the main room (it will be different, you will see a telescope on the upper path), go down the hallway where the save point is to reach her and complete the quest to unlock the achievement.