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The Penghu archipelago is primarily composed of basalt, formed when lava repeatedly erupted from subsurface fissures and cooled on the surface. The earliest volcanic lava flows date back to about 18 million years ago, with volcanic activity largely ceasing around 8 million years ago. Basalt has shaped the flat‑mountain terrain of Penghu, with steep surrounding cliffs. Over time, weathering, wind erosion, and marine erosion have produced a variety of unique landforms. Additionally, rapid cooling of the lava generates tension that causes the rock to fracture into multi‑angular columns—these fracture surfaces are called columnar joints. These joints can be straight, curved, or inclined in various directions, giving the basalt landscape of Penghu its distinctive character. In Magong, on the left side of County Road 201 heading towards Fengguo, you can see towering blue‑bay basalt columns standing beside the road. The basalt of Penghu, shaped by long‑term weathering and erosion, displays diverse appearances; the blue‑bay area is one of the most striking examples of columnar basalt. At Blue Bay, visitors can not only admire the majestic, solitary basalt columns but also enjoy the scenic coastline. **Suggested duration:** 1 hour