On your travels, you’re likely to stumble upon two small islands (one of which is the western-most point on the world map). The names of these islands are the Island Closest to Heaven, and the Island Closest to Hell. Both these islands have extremely powerful monsters, who provide a great deal of EXP to your characters when they are defeated. Defeating them, on the other hand, isn’t always that easy. One way of doing it (if you’re not very strong) is to always flee the battles right away, just waiting for Odin to use his powerful Zantetsuken attack. This is clearly the cowards way out, but it’s a great way of getting easy EXP!
Please note that EXP isn’t the only reason to head to these islands; they are also covered in rewarding and powerful items – check them out.