The Satsop Nuclear Power Plant was part of a larger effort to provide power to the Pacific Northwest. Construction started in the late 1970s and was ultimately abandoned before completion.
These days it's a business park, with normal office space, big warehouses, as well as some interesting use of the tunnels and buildings for fire/military training, movies, etc.
I went as part of a photo outing with pcnw a few months ago. It sounds like it's pretty easy to schedule a group tour of the buildings (with some cost involved) if you are in the area and want to check it out (it's a few hours south of Seattle).
Since we were moving to New York, I thought this would be my last big photo trip in Seattle, so I brought way too many cameras, including my huge 4x5, which I regret lugging around (although I still haven't developed the film, so who knows!).
I was pretty happy with how my instant photos came out! I still have a ton of fun with the instax, and it's so nice to have the prints right away to share.