Xiaomen Islet is located in the north of Hsiyu, away from a 20-meter wide water passageway, and connected to a bridge. On the contrary to its small size of only 0.5-square kilometre, Xiaomen Islet features every characteristic of the Pescadores. It is also known as the outdoor geological classroom. Xiaomen Islet is a lava plateau with a slope descending from north to south. Its southern end is a crowd of villages, and basaltic cliffs are made up of the other three shores. Here, it is easy to observe the ball-shaped porous basalts, the unique iron quartz sandstone, iron clay layers, fossil-doped shell limestone, and water-eroded bad terrains. The famous "Whale Cave" got its name from its physical resemblance of a whale appearing from water. The Whale Cave was originally a basaltic cliff. After years of erosion, it has now become a sea-eroded arch. Nevertheless, beehive-type vegetation fields can also be found in Xiaomen Islet. Surely, don't miss the "Xiaomen Geological Museum" of its geological secrets and history.