The Vast Plains is an area accessible from a needle with a black thread in the Needle Maze.
The Vast Plains is a short, linear area that begins with a large mountain and leads to Dessert World. The area has a grassy landscape with distant hills and a white sky with faint blotches of red, green, and blue.
Left of the area's entrance is a lone cookie NPC sitting at one of the path's ends. Interacting with this NPC will give Sometsuki the "cookie" Window Type. Heading right of the area's entrance instead will lead to an empty path that ends in two cake pillars. Traveling through the pillars leads to Dessert World.
NPC that gives the cookie Window Type