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. They give you a bracelet that has a chip in it to keep track of your purchases. Tattoos are not allowed, but some of my friends covered themselves up with a small towel and had no issues. I really enjoyed the experience and would go again. In addition, there is plenty of other attractions in the area! There are several train stations around Tokyo Dome City. I arrived at Suidobashi station and it was about a 10 minute walk to the spa. The entrance fee is ¥2565 for adults. Open year round from 11:00 am to 9:00 am. – Danielle Kirby, February 2013.
For information about enjoying onsens in Japan check here: Onsen: Japanese Hot Spring Baths