There's no actual grass in Grass World.
Grass World (若葉, Wakaba, Young Leaves) is an area accessible from the stairway portal in the Gray Road.
Grass World is a large, barren area resembling a dirt field. The area is decorated with small plants, rocks, and red lampposts dotted around the area.
Descending the staircase from the Gray Road, you'll come to a small room with a one-eyed creature sitting on a couch. Whenever you enter this room, it may be either sleeping or awake.
Continuing through the doorway to the right will take you to a short hallway, overgrown with plants. Further down the hallway is a dark, narrow path. If you equip the lantern effect here, you will see many strange tubular plants on either side of the path. Walking to the end of the path leads out into the main area of Grass World.
From the dark path, you will come out of a grey concrete building, the main entrance, into the main area of Grass World.
Slightly east of the main entrance is a large cluster of plants and rocks, grouped around 4 lampposts, with a pair of blue pillars in the center. To reach the pillars you will have to work your way around through a hidden path in the plants, starting from the northeast side. When you reach the center, walking through the pillars will take you to Floating Stones World.
Just south of the main entrance is a seemingly inconspicuous cluster of plants, with 4 lampposts marking the entrance. Walking inside through the lampposts and across to the left among the plants will change the area, and you will find yourself on a winding path made of plants and rocks, surrounded by flickering lampposts.
At the end of the path is a dark blue building similar to the main entrance, which will take you to a strange room with a bench and a crooked, dead tree. Rarely, you may be taken instead to a peaceful room with a bench beside a Japanese stone pond, where Urotsuki can relax.
On the far east side of the area is another concrete building similar to the main entrance, with square holes in its walls. Walking into this building's doorway will change the area, and you will walk back out into a winding path of plants and rocks. At the end of the path is another pair of blue pillars that will take you to Green Neon World.
On the same side of this area, just before the concrete building with the holes, is a cluster of plants hiding a small four-leafed plant that will take you to the Warehouse if you interact with it.