Here we provide you some experiences of level 48-54 in Atlantica, the Bran Castle, have a look.
The bats are annoying and aren't worth training at. Starting at Bran Castle there are more than one quest chain. You will also get a huge increase in gold reward per fight as well. One is the main story quest, and the other is a side story that parallels the main quest so you can do both at once. The side story offers good rewards on the side in addition to money and experience.
The side story gives you 300 Iron Doll summons for your Beast Trainer. Quests at this point also start providing stamina per quest. Starting from Bran Castle, you will also encounter mini boss mobs on occasion that have a high drop rate for boxes but have a large amount of HP and a decent attack power. They also tend to be about 10 levels higher than the recommended level(Atlantica powerleveling) of the dungeon.
The first good training spot is at the Hell Hounds and Cerberus near the entrance to the second floor. The mobs here have low damage and low HP. The second spot is in the Bran Castle Jail. The Iron Doll Magicians and Iron Doll Warriors have low damage and good drops. The Magicians are weak against physical while the Warriors are weak against skill(atlantica online gold). Take out the Magicians first because they can use Beast Summon.
The Shadow Jail is a fairly good place to train too. If you have a group of 3 the final section before the boss is good. Alloy Dolls follow the same set up as the Iron Dolls. If you're in a group of 2 the second floor is the best because those guys are weak but the drop rate is noticeably lower. If you did not need to grind before, chances are this will be the first time you need to grind before you can fight the boss or go to the next dungeon.