Onsen in or near Tokyo

If you plan on going to an onsen in Tokyo, the most convenient ones are the more touristy Oedo Onsen Monogatari in Odaiba, or Urayasu Mangekyo or Manyo no Yu in Yokohama. 

If you have more time, visiting onsen towns like Atami or Ito on the Izu Penninsula is recommended. Or inland, you can go to towns like Ikaho, Kusatsu, or Kinugawa.