You need to finish all of the storyline quests. The side quests are optional, but it's recommended that you do them, as they give a lot of experience, gold, and equipment that can be used or sold in the Bazaar and the shops.
You have to do all of the main quests and then you go into the royal muesuem. Then you must do Counterweight east, Counterweight West, and Big Ben. In Big Ben you will fight the final boss named Meowararity.
Mason Sandtamer level 36 Sorcerer and Diviner in The Village of Sorrow
