Not to see my car built (as I did that!) but when I collected it from Dartford after some warranty work, I was taken down the production line and had a good chat about all things 7-related.
Similar to the above, I had some work done there and they asked me if I'd ever had the tour, and if I'd like to! So they showed me around the production line, the repair/service section. Really nice guys and very much enjoyed seeing where my car would have been built.