Odaiba is a man-made island in the outskirt of Tokyo. Its located near the Tokyo Bay, and its a nice place to watch sunset. From the waterfront, you could see the Rainbow Bridge. There are several landmarks you can go there.

1. In front of Diver City, there is a live-sized Gundam statue and during night time, they will play a short movie with the mall as the background, and the Gundam move accordingly. You can stare in awe or enjoy your time in Gundam cafe (I prefer standing with the crowd, taking video and just admiring the Gundam which just felt unreal for me).

Gundam Statue in Real scale (plaupla)

2. Liberty Statue
At the park near the waterfront, there is a mini statue of Liberty, which would feel interesting since it made you felt like in New York, but you're actually in Japan. Its unbelievably crowded there, especially near sunset since everyone wants to take a picture with the Liberty statue in their background.

Odaiba sunset (plaupla)

3.  Palette Town
If you're into amusement parks, then Palette Town might be just the place for you. The ferris wheel looks beautiful with at night.

Odaiba offers the theme park near Tokyo area, might be a good option for those who travels with family.

Ferris Wheel (plaupla)

Reference:
https://www.gotokyo.org/en/tourists/areas/areamap/odaiba.html