If you're burned out from sightseeing and just want to kickback and have some fun like the locals do, you'll find what you're looking for at Tokyo Dome City, a massive entertainment complex in the Bunkyo district.
The area's centerpiece is the Tokyo Dome: the world's largest roofed baseball stadium. The dome, also known as The Egg, is the home stadium of the Yomiuri Giants and Nippon Ham. It can seat up to 55,000 people, and often fills up for popular matches. If you have a chance, catching a game offers a uniqe insight into Japanese sports culture.
Also in the area you'll find a small but fun amusement park (the roller coasters are a highlight), an arena for boxing and martial arts known as Karakuen Hall, a 43-floor hotel, bowling center, shops and eateries. A recent addition is the LaQua Spa onsen complex.