Lv 21-25
Map: Skeleton Hole
Monsters: Mean Skeleton, Skeletal Archer, Freezing Skeleton, Skeletal Demon Archer, Skeletal Warrior, Undead Priest, Corrupt Skeleton and Undead Mage
Elite & Boss: Freezing Skeleton (Elite), Skeletal Demon Archer (Elite), Skeletal Berserker (Elite), Undead Mage (Elite) and Skeletal Horrorl, the Death Warrior (Boss)
Monsters Info: Attack types vary
Related Quest: Accept from NPCs in main city
Related Preparation: Bring abundant intermediate potions and a certain amount of advanced potions. Very likely, it'll not be a luxury.
Suggestion on Level Up: Take care with Skeleton Hole! To get  Magic World Online Gold  through, you may choose to team up with others. And it may be even more dangerous to solo deep into 3rd floor of the hole. The powerful Skeleton Boss in there is not the kind to sympathize with a weaker life.

Lv 22-30
Map: Shadow Forest and Dragon Vale
Monsters: Giant Mantis, Anthropophagy Flower, Devildom Mantis and Virulent Anthropophagy Flower
Elite & Boss: Crazy Mantis (Elite) and Crazy Anthropophagy Flower (Elite)
Monsters Info: Active attackers, dealing physical and skill damage
Related Quest: Accept from NPCs in main city
Related Preparation: It'll be good to prepare enough intermediate potions.
Suggestion on Level Up: Practice makes perfect. Experience on this map shall qualify you as a skilled player.

Lv 28-34
Map: Hawk Fall and Sky Garden
Monsters: Trogg, Werewolf Warrior, Forking Trogg, Werewolf Ripper, Similodon and Hell Tiger
Elite & Boss: Crazy Trogg (Elite), Werewolf Ripper (Elite), Crazy Hell Tiger (Elite) and William, the Demon Wolf King (Boss)
Monsters Info: In addition to the physical damage, these active attackers also do skill damage.
Related Quest: Accept from NPCs in main city
Related Preparation: Prepare abundant intermediate potions and some certain amount of advanced potions. It's not a luxury though.
Suggestion on Level Up: Higher level monsters does not always mean higher difficulty to deal with. Compared with Skeleton Hole, monsters here live in a spacious area not being so close to each other. So it is easier to pick them one by one. But if you want to offend Demon Wolf King, you'd better psych yourself up for its one hit kill.