Okay first you have to enter the castelia sewers and then when you are trying to go south you will see some stairs.Enter the stairs and you will see the castelia park where there will be grass.
DIRECTIONS:
Enter the sewers and go straight.turn left,walk for some distance,turn downwards towrds the plank floating on the water and to your left side there will a stairs.Enter the stairs and you will enter the park where the grass will be.