Iwaki City Coal & Fossil Museum, usually called Horuru, ties together two local stories: the Joban coalfield and fossils found in the area. The displays include mining history, a recreated mine experience, and the Futabasaurus plesiosaur discovered in Fukushima.
It is a good pairing with Spa Resort Hawaiians because the museum explains the industry that came before the resort. Visit it for context, not just for the dinosaur skeleton.