Izumi Tenku no Yu is a 24-hour spa directly connected to Haneda Airport Terminal 3, featuring around a dozen hot springs and baths. Relax in the outdoor bath while watching planes come and go, and even catch a glimpse of Mt Fuji on clear days. There are also plenty of couches and reclining chairs, plus dry, steam and stone saunas.
It costs ¥4,800 for adults (¥4,000 between 1am to 5am) and ¥2,000 for primary school students and under. The admission fee includes a face towel, bath towel and access to the entire facility. Those staying at Hotel Villa Fontine receive a ¥2,000 discount (¥1,000 for children).
Note that baths are not available between 10am to 1pm daily, and that hotel guests have priority entering Izumi Tenku no Yu if the facility reaches capacity.