Once you have beaten the elite 4 and got the national dex, go to the lake near pastiora, go up the route a bit and there will be a place that wasn't there before. go into the cave and keep going through random doors and eventually, you will find giritina (not origin form)
(edit by awso78) the place that wasn't there before that he talks about is spring path and the cave is turn back cave. it is best if you go to the lake from veilstone because spring path isn't in the lake, its on the way to the lake from veilstone.
Get an action replay
You can find Cyndaquil at Mount Stark on Pokemon Diamond.
you dont, only on dimand. trad!!!
you find him in the old chateu in the ilex forest
Save in front of Giritina and battle it. if it isn't a shiny, turn off the ds and try again. It will take a long time.
It is where you find Giritina. I recomend going straight through the whole cave and u will eventualy get to giritina. Good Luck :)
you have to beat Cyrus in the distortion world
you need to dfeat the 4th gym leader
After you go and beat the elite 4, make your way to spring path. you will find the Griseous orb. give it to Giritina and he will change forms.
If you can't find the exit, try using an escape rope.
To find it go to spear pillar and you will battle the commanders and in the distortion world at the end is where you find Giritina! I'm not sure about the item though and a good walkthrough website is http://www.psypokes.com/platinum/walkthrough.php
you get giritina in the distortion world. It really is quite simple