To start this you will need HM's:Fly and Rockclimb
To get Girantina you would have to beat the elite four and claimed the national dex. Fly to veilstone city and go down to route 214. Now go down and stop at Psycic Abigail. Now go right and down again you will see a smmall patch of grass. Go strait through the patch of grass amd then you will see a fatman walking up and down go past him so go down and turn rightyou will see a lady standing there now go down into a small block. There will be another person walking up and down go down past her and you will see a path through the trees. It will be called spring path follow the path into sendoff spring. You will need to go through the small grass use Rockclimb up the mountain go to the other side of the mountain and use Rockclimb again into a cave.
From here there is a maze you will be able to do
Thankyou for reading
Please rate me it's my first hint
By Pokemon coder