it is athe end of route 224, and it unlocks shamin when you bring the oak's letter to it you get it at an event
He goes to Route 224...
At the end of route 224 is a white rock. When you have Oak's letter you can do somthing to the rock and then the area around the rock will be filled with flowers and a Pokemon will appear and go to a path to the north that juatr appeared.
You can't access Route 224 until professor Oak upgrades your Pokemon. Then go east of Victory Road. Route 224 is the eastmost Route in Diamond Pearl and Platinum.
After you gain Oak's letter you can go to route 224 and catch shaymin
Route 224 You need to use the pokeradar Theres a 2% chance of finding one
First, go to the Pokemon Leauge.Then, right above the Pokemon League is route 224
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You find Shuckle on Route 224 after you get the National Dex and you have Pokemon Emerald inserted in Slot 2 on the DS.
After you have beaten the Elite 4 and Champion, you can access Route 224. If you enter Victory Road from the northern entrance by the Pokémon League, you will be able to get to a cave that was previously blocked by a man. Go into that cave and through it, and you will emerge on Route 224.
it leads to another section of the cave, which exits on route 224
The pokeradar!