After reaching level 1000, a new realm will be unlocked called the “Eternal Plains” this realm contains much harder monsters but better experience gains.
The realm is split vertically with the top half of the map being lands controlled by the Irellians (a race of human like beings that evolved wings) and the bottom half being controlled by the Subterrans (a race of beings that spend much of their time underground) … there is a small band along the center of the map which is controlled by the Arterians (the artifact builders who vanished from the normal realms many moons ago).
There are monsters ranging from level 1100 to 1500 (and maybe even a few higher), killing these monsters stands a chance for you to gain a special item, be it a feather or a shedding. These special items can then be turned in at one of the main towns to unlock special rewards.
Killing the monsters in this realm should be a lot harder than normal monsters but will yield a lot more experience, these monsters may also have Demonic powers so should not be considered weak.