FamilyAir is right about Krokopatra but I would still do all of quests and side quests. It took me over 2 months to complete Krokotopia and I got to Marleybone at Level 31. . Just do all the quests and side quests .
You need to complete ROyal hall, chamber of fire, palace of fire, to get to the kroksphinx. Once you finsh everything in the kroksphinx, you move on to the tomb of storms. Once you complete the tomb of storms, you get to defeat krokpatra and go to marleybone. You must do all story line quests(NOT side-quests) to defeat krokopatra and arive at marleybone.