Odaiba is a man made island in Tokyo Bay. Here you can engage in typical Japanese recreational activities such as shopping and entertainment, or take a stroll along the coastline. Odaiba even has its own Statue of Liberty at the waterfront with the beautiful Rainbow Bridge in the background.
When I was visiting Odaiba, the island appeared rather deserted, but it lives up on weekends, when people from the Tokyo area come to visit. There are several large shopping malls on the island and the Yurikamome transit line makes the ride from more central parts of Tokyo to Odaiba really smooth. The Yurikamome transit runs most of the time over ground level, so remember to bring your camera and get some beautiful shots of Tokyo.
One of the most famous buildings in Odaiba is Fuji Television headquarters, which most of all resembles a futuristic space station. Inside the building, you can buy different kinds of merchandise or visit the observation deck, from where you get a view of Mt. Fuji, if you are lucky.