Cool place would 100% recommend. This place deserves more visitors!
When we arrived we felt like we were in the wrong place, only a security guard in sight. We went through the gate to the visitor center and had the best time. Jon, a very friendly tour guide, was just about to start his 15:30 tour and we were the only visitors. He told us all about the history and operations of the plant. We could see two of the turbines up close, even at different heights.
There's also a little side building with lots of info about the fish and fishing methods of the native americans. It includes underwater windows so you can see the fish swim through the ladder, we saw lots of salmon.