At level 50 if you attack the mobs in the city I am getting anywhere from 3 to 5 levels an invasion and up to 10 for doing a set of them. If you attack the mobs though. And if a couple of you do it you get xp for all they kill too so you can spread out and get even more xp.
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Or open it and sell it and it still sells for the level 100 prices even though scaled down to your level. Getting 60g a weapon or 30 gold a armor piece ain't bad for a low level.
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Also make the one of the main cities in panda land your home and one can get anywhere. I always do this on alts just need to have a friend or guildie willing to take you there or pay a Mage