How do you catch girantina in Pokemon Diamond?

Well first you need to Beat the Pokemon league and then you go to that place next to the cave where the ruin maniac is and search in the grass but not the tall grass the thin grass that you always travil on to get to places and go to the hidden cave in the right and keep on going through the path and when you go through the woods at the end of that path you keep going to the tall grass and when you go to the end of the tall grass you go up and use rock climb in the same type of terran you usually do to use the move rock climb and when you get all the way up go to the right and when you see the place to go rock climbing down. And when you get down there I need you to go through the cave in the front.And continue to go through all the caves in front. You even hit some ruins along the way and after you go through all the caves you will go down a flight of stairs and there Girantina is in front of you. Even though that cave that you go through is called turn-back cave, don't let it fool you! If this doesnt work for you than e-mail me at Pokemon.princess2009@live.com and it would be easyer for me to help you! Hope It helped. It took me a while to type this so i hope its worth whaile!