In the Dead Crater location, there is an Obelisk that you can use to gain additional experience.
Only one member of the group can touch it, and only once during the lifetime of the instance.
For the obelisk to work, you must kill at least one mob of level 11+ (scorpions are not suitable). Depending on the number of monsters killed, the amount of experience given out will vary (so for one Spirit Worker they will give 500 experience).
Maximum experience (10,000) can be obtained by completely clearing the Spirit Plateau and Dead Crater.