In & Around:
This is a popular location for photographer to go get Mt.Fuji behind factory area in Kawasaki. See location map below.
Observatory floor is on 10th floor and one side of the window facing south which happen to be the same direction as Mt.fuji. In fact, the Sun will set right behind Mt.fuji and you can get the sun perfectly on the tip of Mt.Fuji from here. I was a bit late (40-30 minutes before sunset) when I get there and it was my first time there so I didn't expect to see this, The window was packed with photographer and I could find a space for myself. Next time I will go early.
Tripod is allowed and it is free. However, it is a kind of very far from city. If you are not familiar with the place, I recommend you to go there with local people.