all you need to do is get on level 15 and go to cyclops lane if your below 15. then do all the quest for that myth kid nolan stormgate i think thats what his name is you'll know then you will have to go talk to merle ambrose and he will give you a quest and do that then you should be able to unlock it :-)
Your level doesn't matter. Once you completed the main storyline in Colossus Blvd, you will be given the quest to see M.A. He will than give you the key to krok.
well after you complete all of wizard city you are asked on a quest beat nightshade then when you beat nightshade you are sent to krokotopia p.s. you do not need to beat the sunken city
after you kill lady black hope talk to sergent muldoon then take all the new quests. when you are done with all of them go to the headmaster. do not do collasol trouble to a look of horror. you need to fight foulgaze in olde town. then fight lord night shade after talking to the headmaster after foul gaze. fo beating nightshade he will send you behind the water fall to find the real deadth school. then you learn a new spell fram merele ambrose. he will send you to bartleby. he will tell you to go inside him and go through a door and click on krok and you will be in krokotopia
