Tiezhu Islet Introduction
About 2 kilometers north of Da Bai Sha Yu, there is a typical flat-topped island shaped like an anvil. Most of the island is composed of large flat slate stones, smooth and unmarked, resembling an anvil used for forging, hence the name "Tie Zhen Yu" (Anvil Island). The island is approximately 5 meters high and surrounded by vertical sea cliffs. Apart from the anvil-shaped basalt, there are also many uniquely shaped honeycomb rocks. Due to its use as a military shooting range in the 1950s, remnants of metal scraps and rock fragments can still be found here. Tie Zhen Yu is located offshore to the northwest of Penghu Main Island and is entirely made of basalt, resembling an anvil, which is where it gets its name. Due to the northeast monsoon in winter, the waves have eroded the northern coast of Anvil Island, creating a sea cave over 10 meters deep, which is the largest sea cave in all of Penghu. This cave has a unique position and is unable to receive sunlight for many years; therefore, even in summer, the temperature inside the cave is about 3 to 5 degrees Celsius lower than outside, frequently attracting visitors seeking a cool respite, earning it the name "Air Conditioning Cave." From the northern sea, one can clearly see that the upper part of the island's cliffs is made of basalt, while the lower part consists of volcanic breccia. Due to the weaker nature of the volcanic breccia, it erodes under the winter sea waves, forming a massive sea cave beneath the northern cliffs, which can be accessed by small yachts and fishing boats. The intertidal zone of the island is relatively shallow and short, with almost no erosion platforms near the sea cave. Only on the eastern side of the cliffs is there a platform about 5 meters wide, along with small pebble beaches on the southern and western sides. As a result, there are fewer fishermen collecting snails and shellfish, allowing over a thousand common terns to gather and breed on the island each year. Whenever boats approach the shore, flocks of common terns will take off from the island, emitting a low barking warning call that resembles that of a small dog. Eventually, they all gather above the boats, circling in a very remarkable display.
