The Battle Tower...accessible once you have defeated the Elite Four, your father will give you a ferry ticket which will allow you to go there.
The Battle Tower is exactly what it's name states...it's a tower in which you battle. You battle trainers in streaks of Seven...you need to try and beat all the trainers to get the better prizes, that's all there is to it...for more information use the Menu-Bar above to access the pages
 
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