Glad somebody created a thread on this.
A friend and I went on the B Reactor "tour" in 2016. Super-mega-highly recommended, especially if you're any kind of history/science/technology geek. I put "tour" in quotes because they basically bring you to the building and turn you loose. There are scheduled talks in different areas, but it's otherwise unstructured, and you can just show yourself around. That was a pleasant surprise--very much a UE-er's tour format.
If you're interested in going, start watching the tour registration page in March:http://manhattanpr...actor.hanford.gov/
Somewhere between March and April, registration will suddenly open and suddenly fill up, so you have to be vigilant about checking the page or you'll be waiting another year.
In addition to the B Reactor tour, there are other Hanford tours that, for example, take you to the cleanup sites and explain the work going on. I'm hoping to go back and do one of those this next year.