You get to walk above the production line and see the cars being made. They also have a video explaining the entire car-making process. The tour guide spoke good English and was very informative. Part of the tour includes visiting the museum but I don't think you can visit the museum alone since it's well inside the Mazda Factory campus.
We also visited the Toyota Factory in Toyota, Aichi Prefecture and we thought that it was more impressive than the Mazda factory. But if you're in Hiroshima I highly recommend visiting the Mazda Factory.
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