One definite item on our TODO list was visiting a Japanese Onsen. Most of these natural baths are actually gender separated, so ti took a bit of effort to find one suitable for couples, but we found one in Nerima Toshimaen Niwa no yu .
The visit was just perfect with coom area for men and women both inside and outside with great athmosphere. In womens section you also had more baths and it was really a place where I could spend an entire day.
Our visit to the area was perfected by restaurant visit afterwards: we visited a local Japanese BBQ / Yakiniku place: Tonyo Chokusho Yakiniku