Many people don’t realize this but there used to be an onsen under Tokyo Station. It was called Tokyo Kur, open to men only and offered baths, shiatsu and akasuri massage. Sadly, it has closed.
Excerpted from the Japan Times, Sunday, Oct. 7, 2001:
Tokyo Kur by Tokyo Onsen — This sauna-spa is for men only. It features baths, a mist sauna, jacuzzi, a reclining bath with micro aqua jets and a relaxation lounge. Akasuri and massages are available.