Visions of Mana

You will find both lesser and greater elemental aeries in the world. The lesser ones can be challenged as soon as you receive the elemental vessel of the same type, and simply consist of two waves of enemies that must be defeated within a certain amount of time. These challenges are synced to your character level, so it doesn't really matter when you try them. Once you complete all the lesser aeries of a type, you can then challenge the greater aerie, which consists of 2-4 waves of enemies of generally high levels, so these are best left until you've completed the game and tracked down all the Nemeses for the extra experience. Some of these have very short time limits and somewhat specific damage types may be required, so play with your party composition and classes for best success, and always go in with a full Class Strike gauge as this can wipe out a full wave of enemies at once.