Spa LaQua is an onsen in the middle of Tokyo Dome City. They have multiple mineral pools, some with jets. There is a steam room, places to eat, get a massage, have your nails done, watch TV, and sleep. It is a great day spa. Massage, nails, and food are additional costs.
Shinjuku (新宿) is a central ward of Tokyo, known as the metropolis' second center (副都心, fukutoshin). The area surrounding Shinjuku Station is a huge business, commercial, and entertainment center located atop the world's busiest railway station complex.