Where is the fighting arena in Pokemon diamond?

when you defeat the elite four go to snowpoint talk to the man who says he wants to carry a great trainer recogniseed by the elite four on his boat and he'll take you there. its a place 2 fight when you defeat the elite four go to snowpoint talk to the man who says he wants to carry a great trainer recogniseed by the elite four on his boat and he'll take you there. its a place 2 fight