For players of Richard Garriott's Tabula Rasa, gaining levels in the late teens can be difficult. The folks at Massively.com have posted a video showing a great place for grind out lots of experience. Executed carefully, a Fithik free-for-all can be very fruitful.
It's a closed off area chock full of bug-eyed Fithik aliens with weak electric resistance. The layout of the Fithik mobs allows for you to easily ramp up your XP modifier to 250%, and sustain it almost indefinitely.