Pal Park

[Final Smash]

Where is the Pal Park on pokemon Diamond I cant find it anywhere!

[Smouvy]

Clear up to the Pokémon League, complete the Sinnoh Dex, then you'll know where it is

[Cobelcog]

If you've done all that and still don't know where to go, surf south of sandgem and follow those routes.

[Blobulator]

Originally Posted by Smouvy

Clear up to the Pokémon League, complete the Sinnoh Dex, then you'll know where it is

If you can get a friend to trade/trade back the other legendary (in the OP's case Palkia I guess) you don't even need to beat the Pokémon League. Completing the Sinnoh Dex and talking to the professor should be enough, I remember doing it myself accidentally, heh, before I knew they show you a picture of the other legendary at the end of the league.

But yeah, surf below Sandgem and follow it along, then onto the land bit and to the top right is the entrance of Pal Park.

[Porky]

an old woman shows a picture of the other legendary in celestic town after you catch Palkia/Dialga, so you don't even need to trade

[Blobulator]

Originally Posted by Troll clowns

an old woman shows a picture of the other legendary in celestic town after you catch Palkia/Dialga, so you don't even need to trade

Yeah, was just saying incase they hadn't beaten the league yet. Some people prefer to do it that way so they can get their old pokemon to use against the league rather than be stuck with only what they've gotten throughout that game until after.

[Ozimul]

All you have to do is "see" all of the pokemon and then visit Prof. Rowan to get the Dex. So if you get to Cynthia and see all of her pokemon but get killed you can still go get the National Dex. Then head south from Sandgem and then east. You'll get to the route with Pal Park.

[Smouvy]

Originally Posted by Danny Trabajo

You need to do the League anyway because that's the only way you'll see some of the others, though...

No, there is no pokémon there you couldn't have seen before.