Once you've completed your second visit to Traverse Town in Kingdom Hearts: Final Mix, you will gain access to more worlds in your search for King Mickey and Kairi. The first world you will come across after having the Navigation Gummi installed is Agrabah. Despite being a relatively small area, Agrabah is tricky due to how things have to be done in an exact order that is not clear. Before starting Agrabah, it is highly recommended that Sora, Donald, and Goofy should at least be Level 20. If you need to level up a bit, Traverse Town is a great place to do it.