Grandia

Easy level up for water magic
If you reach a save point don't recover right away. Take any character with water magic and spend all of their MP casting healing spells. This will give you Water magic experience points. Then step on the save point and recover.
This way you can get water experience, but recover the mp right away.
OR

Near the entrance to the Dio ruins there is a save point very close to a wall trap. Run into the trap and heal yourself with water magic as long as you like. You can get very high magic levels very quickly.

Hidden Mission
To access a bonus stage, go to the Zil Dessert on Disc 2. In the southern part of the desert, there should be a path in the canyon wall that leads to the castle of dreams. (If you still cannot find it, go south from the desserts exit alog the wall.) This area is just a place to gain exp and obtain the Lightning sword.