Once you enter Disney's Magic Kingdom, you will first arrive at Main Street USA. You need to walk through Main Street USA to get to Cinderella Castle.
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Adventureland is to the left of Main Street USA but it is hard to get to Adventureland from Main Street USA or the entrance of Magic Kingdom unless you know short cuts or you take the train. The Disney World's Magic Kingdom map would have you walk almost to Cinderella Castle and then turn left.
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Frontierland is on the left hand side of the Magic Kingdom park, after Adventureland. In Frontierland, you will find the famous Splash Mountain ride, Big Thunder Mountain Railroad ride, Tom Sawyer Island, and Country Bear Jamboree.
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