Niwa-no-yu is a large sento-style bath complex beside Toshimaen, with indoor and outdoor baths, steam rooms, Finnish saunas, and a relaxation area upstairs. It is polished and more resort-like than a neighbourhood bathhouse, making it useful after a long day crossing Tokyo.
Bring a swimsuit if you plan to use the pool area. Food, drinks, and massages cost extra, and children are not admitted.