Still in Tokyo prefecture, but some way removed from the hustle and bustle of the city is Seotonoyu. It takes a while to get there from the centre of Tokyo, but it's a nice relaxing place to come when you have the chance.
We took the 800 yen per person course for three hours use of the facilities. There's an indoor bath, as well as an outdoor bath (rotemburo), as well as a sauna.
If you so wish, you can actually stay there, and there's a cafe, restaurant and gift shop there as well.
For me anyway it was nice to escape the city and relax in some very pleasant surroundings.