The plains is a wide, open area with several different types of new enemies, more Gathering nodes, and lots of treasures. The northwestern portion of the plains is accessible only by exiting to the SW of the capital. Refer to the map above for the location of these chests and resource nodes.
The paths leading to the other areas are inaccessible at the moment so it’s recommended to continue to the capital after looting all the chess and resources nodes OR after spending some time farming off the enemies for extra EXP, fol, items, and SP. Fiore deals really high damage at this point of the story so it will be easier to farm around groups of enemies with her around. Continue to Central Resulia once you're ready to proceed with the story.