If you are visiting Tsuruoka, Yamagata (山形県鶴岡市) in August:It's a bit late to see alpine plants on Gassan (月山). (It's still nice, though)
Don't forget to bring your bathing suit.
But, can't miss "Dadakko (だだっ子)", the best selling sweets of Yamagata. It must be named after "dadacha-mame", Yamagata's specialty green soybeans. But, "Dadakko" also means a spoiled, unmagageable kid. So, don't be Dadakko even if you miss the best season to see alpine plants and forget a bathing suit. Oh, and unseasonal "summer" oysters are good as well.