Where is Dialga in platinum?

Answer 1

When you are on the outside of Mt.Cornet climb up the first set of rocks and go through the door on the left.Then up the waterfall through the door you will find two poke ball things collect them then go to Sandgem talk to Lucas he will tell you something about Celestic go do what he said. Then go back to Lucas and he will tell about Pokemon at the spear pillar when you are at the spear pillar you will see the Pokemon catch him the go back through the door you came in turn around and go back to the spear pillar and there is the other Pokemon.

Hope this helped!