Round sulfer works
Round Sulfur Mine is an intermediate grind-zone. Sulfur mobs are primarily grinded for money. The xp here is decent but nothing special. With that being said, this spot is decent, you can grind Polly's for better, more profitable rewards. Polly's is also one of the best spots in the game for xp.
Round Sulfur Mine is located North of Valencia in the desert; The desert is located East of Altinova, the fifth major city in Black Desert.