Xiaomen Island is a small outlying islet at the northern tip of Xiyu, covering roughly 0.22 sq km and connected to Xiyu by the 168-metre Xiaomen Bridge. The entire island is composed of basalt, and its coastline has been shaped by wave erosion over tens of thousands of years into the densest, best-preserved concentration of sea-erosion landforms in the Penghu archipelago. This is not a beach destination; it draws visitors with an interest in geology and photography, and also suits families looking for a half-day educational outing combining a museum visit with outdoor geological observation. During the northeast monsoon in winter, water jets shooting from the Whale Cave have become one of Penghu’s defining winter photography subjects.
Highlights
The Whale Cave sits at the base of a sea cliff on the north side of the island and is classified as a sea cave landform. Long-term wave erosion has carved an arched passage through the basalt wall; viewed from certain angles above, the outline of the entrance resembles a surfacing sperm whale, giving it its name. In milder seasons, visitors can look down from the viewing path to watch seawater surge inside the cave. The most striking conditions occur during the northeast monsoon season (October through March): ocean swells drive into the cave mouth and are expelled by air pressure, shooting water jets several metres into the air — excellent photographic material when caught in raking light.
Continuing along the path beside the Whale Cave toward the northern sea cliffs, visitors encounter near-textbook examples of columnar jointing. Pentagonal-to-hexagonal basalt columns stand vertically, with individual shaft diameters ranging from roughly 10 to 30 cm — the geometric result of magma cooling and contracting slowly on the seafloor. At low tide, a wide wave-cut platform is uncovered, filled with pools of varying sizes where shore crabs, sea anemones, brittle stars, and other intertidal life can be observed closely, adding a biological dimension to the geological experience.
At the bridge approach, the Xiaomen Geology Museum uses illustrated panels and rock specimens to trace Penghu’s volcanic geological history, from seafloor basalt eruptions around 18 million years ago through to the ongoing sea-erosion processes visible today. The exhibits are designed to be accessible, making it a good starting point for families before heading outside to match what they have seen in the museum with the actual landforms. Allow 1.5 to 2 hours for both.
Getting There and Nearby
The most direct public transport option is to alight at Xiaomen Whale Cave stop (PEN299523) and walk roughly 5 minutes to the cave entrance. All buses heading toward Xiyu serve this stop; real-time schedules can be checked on the Penghub homepage. An alternative is to alight at Xiaomen Archway stop (PEN299522 or PEN299524) and walk the roughly 0.7 km from the bridge head north across the island — a good option for visitors who want to start at the geology museum and continue to the cave.
Visitors arriving by car or scooter will find a car park on the east side of the Xiaomen Bridge plaza. Spaces are limited; arriving before 10:00 AM on summer weekends and during the Fireworks Festival improves the chances of finding a spot.
A suggested route linking sights along the west side of Xiyu: Xiaomen Island Whale Cave → Erkan Old Settlement (about 12 minutes by road; Penghu’s only officially listed preserved traditional village, with an intact cluster of Chen family historic residences and a traditional herbal medicine shop near the entrance) → Xiyu West Fort (Qing-dynasty cannon battery ruins, a further 10 minutes by road; a commanding viewpoint over the Penghu Channel) → Fisherman’s Island Lighthouse (the westernmost point of Xiyu, built in 1875, one of the oldest surviving lighthouses in Penghu). The complete route takes roughly half a day and is most flexible by scooter or car.