An ashiyu is a foot bath: a shallow pool of warm water, often from a hot spring, where you sit and soak only your feet. At a foot-bath cafe you order a drink or a sweet and keep your feet in the water while you eat, a good rest after a day of walking. Several are at hot-spring inns, but anyone can drop in without staying, and rolled-up trousers are all you need.
A cafe at an inn in Kusatsu, where the courtyard foot bath is fed from the Yubatake, the steaming wooden channels of hot spring water in the middle of town. Sit with your feet in the water over a parfait or a drink, and warm up after walking around the Yubatake. You do not need to stay at the inn to use it.
A foot-bath cafe run by an old inn in Dogo Onsen, the hot-spring town of Matsuyama on the island of Shikoku, a short walk from the town's famous wooden public bathhouse. You sit with your feet in warm water while you have a drink or a sweet, and no booking is needed. It is closed on Tuesdays and Wednesdays.
A foot-bath cafe inside a hotel in Kinugawa Onsen, a hot-spring town near Nikko about two hours from Tokyo by train. You look out over the river gorge while your feet soak, with a sweet or a coffee in hand, and a towel is lent for drying off. It is usually closed on Thursdays, but listings differ, so check before you go.
A bakery cafe on the grounds of an old inn in Yoshina Onsen, a small hot-spring village in the middle of the Izu Peninsula. You choose bread fresh from the oven, then eat it at a long foot bath with a drink. You do not need to stay at the inn, and no booking is needed for a day visit.
A small foot-bath cafe in a massage salon a few minutes' walk from Ueno Station, where you sit with your feet in warm water and a cup of herbal tea. It fits easily between the museums and the zoo in Ueno Park. Book at least a day ahead, because same-day bookings are not accepted.