The Forest North of Ellinia is one of the most useful places not only for early level training but also for when you achieve Level 30 and need to make the 2nd job advancement.
At Level 30 speak to Grendel who tells you to speak with a colleague of his because Grendel is far too busy.
Head back to the Forest North of Ellinia and go all the way to the top (Avoid being hit by monsters when you are close to the edge of platforms or else they will send you plummeting down) It will take a very long time to get to the top but when you do the reward is splendid.
Speak with The 2nd Job Advancement Instructor who will teleport you to a hidden Dungeon, inside you will find Horny Mushrooms and Curse Eyes, the difference between these monsters and their regular counterparts are the fact that the Horny Mushrooms hit 90+ and instead of the usual 100+ hits Curse Eyes will only do 90+ hits but usually nothing over 100.
It is a bright idea to bring a lot of Hp pots and Mp Pots, also to have a high Level in Magic Guard.
These are the only 2 major reasons why anyone would bother visiting The Forest North of Ellinia.