Tsuruoka sits on the Sea of Japan side of Yamagata, a long way from the standard Tokyo-Kyoto route. That distance is part of the draw. The city has Shonai clan history, serious Buddhist sites, a strange and excellent aquarium, and the sacred mountains of Dewa Sanzan close enough to shape its identity.
In town, Chidokan and Tsuruoka Park keep the old castle-town story visible. West toward the coast, Kamo Aquarium has turned jellyfish into a reason to travel. South and east of the centre are temples associated with the local tradition of sokushinbutsu, monks who undertook self-mummification as an extreme religious practice.
Tsuruoka is also one of Japan's UNESCO Creative Cities of Gastronomy. Dadacha-mame edamame, mountain vegetables, Shonai rice, seafood, and temple food from the Dewa Sanzan tradition make eating here more interesting than in many larger cities. It is worth a spare day if you are already in Yamagata or crossing the Tohoku coast.