you catch him on the cave
some say you can catch dialga in the celestic cave, that's how i got him.
You have to get sandshrew in waywards cave but its also pretty rare to get him in there
Unown (often wrongly spelled as Unknown) is a Pokemon in the Pokemon series. If you catch one of every type, a new part of their cave will be opened.
If you catch 26 Unown in Pokemon Diamond, go to Ruin Maniac Cave. He will be waiting inside for you. You can catch Hippopatos in the cave, along with Geodude. Go to the end of the cave where there is another entrance. Go through, and when you get inside, you will see a writing on the wall. It says, "?!" Those two Unown are in there. Capture them. You now have all the Unown.
soon enough youll venture through a dark cave and at the end there is dialga you will have a master ball by then use the master ball to catch dialga
spear pillar [go to hearthome city and go to the left until you see a cave]
On the cave maps.
you catch him on the cave
You can't catch a Lugia anywhere in Pokemon Diamond.
You can only get Dialga in Pokemon Platinum and Diamond but you can get Giratina at turn back cave and also Palkia at Spear Pillar.
u cant find palkia, but u can get dialga at spear pillar
go strate down from the town with the dialga statue
Yes But Its Very Hard You Need Mesprit,Uxie and the last farie go to the town with the cave in the middle in it and the faries will do something and dialga appears
You catch it in the cave below the cycling road then you go up as far as you can and there should be a cave.
go to turn back cave
when your Pokemon learned surf, use it on a lake. you will see a cave. enter to the cave and you will see uxie,mesprit or azelf.Azelf and uxie will ran away but you will be able to fight with mespit,it will run away and you must chase it with your poketch's map.But you cant catch it until you catch dialga or palkia.