COMMENTS Soak in the Traditional Onsen Experience Izumi, modeled after a traditional Japanese bath or “onsen” features indoor and outdoor Japanese bathing experiences, including steam rooms, saunas, and hot tubs with spectacular ocean views. Exclusively on Diamond Princess®, it is the largest Japanese bath of its kind at sea and offers guests a chance to experience a little of a popular Japanese pastime. Men and women have separate facilities, except for one outdoor hot tub where suits are required.