This attractively laid-out museum gives a good introduction to the volcanic and sedimentary rocks that make up the archipelago. It sits on the slope that leads from Xiamen village past coral-stone walled gardens to the clifftop path. From here, it's less than five minutes to a rocky erosion arch known, somewhat perplexingly, as Whale Cave.
It's worth walking on around the island for more fine views. Xiamen village has a minor charm too and a handful of restaurants catering for tour groups that often have lunch here.