Nearly all the Penghu islands are composed of basalt; the only exception is Huayu, which is made up of andesite, a rock formed by rapidly cooling volcanic magma. Andesite magma is highly viscous and has a slow flow rate, generally collecting in cone-shaped piles near volcano craters, forming topography different from basalt mesas. Huayu took shape about 65 million years ago; thus, it’s the oldest island in the Penghu archipelago and also the westernmost.

Huayu is northwest of Wang'an Island. Nearly a hundred species of plants are native to the island, giving it its name, which translates as “flower island.” Today, only a hundred or so people live on Huayu. Because the Kuroshio and Oyashio currents come together here, the area is a fertile fishing ground, and most residents earn their livings from the sea. On Huayu's eastern half, Yandun Hill stands 53 meters above sea level, the island’s highest point. Huayu Lighthouse is atop a hill on the west side. The pure white tower was built with reinforced concrete; it’s the westernmost lighthouse in Taiwan and an important Huayu landmark.  

You can see Taoist immortal Lu Dongbin's "footprint” on a southeast reef. It's an exact match for the right footprint on Wang'an Island's Tiantai Mountain, but it’s only visible at low tide!