Penghu Islands - Blue Cave

Magong · Penghu County · Taiwan

The Penghu Islands, an archipelago of 90 volcanic islets scattered across the Taiwan Strait between Taiwan and mainland China, offer a diving experience distinct from anything else in the region. Known for their dramatic basalt columnar formations, wind-carved sea caves, and the extraordinary South Penghu Marine National Park, these islands combine geological spectacle with rich marine biodiversity in a setting that feels far removed from Taiwan's bustling cities. The Blue Cave, located on Xiji Islet in the southern archipelago, is Penghu's most famous natural wonder. A semi-open sea cave eroded by centuries of wave action, it produces a mesmerising blue glow when sunlight refracts through the water at the cave entrance. While the cave itself is best viewed from excursion boats, the surrounding waters of the South Penghu Marine National Park offer exceptional diving and snorkelling among basalt rock formations draped in colourful corals. The marine park's signature attraction is its vast fields of purple staghorn coral, a rare formation that creates an otherworldly lavender-tinted underwater landscape. Beyond the purple coral, dive sites across the archipelago feature healthy reef systems hosting stingrays, cuttlefish, sweetlips, and yellowtail barracuda. Shallower sites are alive with clouds of colourful damselfish, blue-striped angelfish, and coral gobies. The deeper sites around the outer islets, such as the Wolf of Donji at 15 to 25 metres, attract larger species and offer excellent visibility. Penghu's basalt geology extends below the waterline, creating a unique underwater topography of columnar formations, arches, and swim-throughs that distinguish these dives from typical coral reef environments. The water temperature ranges from 20 to 28 degrees Celsius across the year, with the diving season running primarily from April through September when the fierce northeast monsoon winds relent. Magong, the main city of Penghu, is connected to Taipei and Kaohsiung by frequent short flights, and the archipelago's compact size makes it possible to explore multiple dive areas within a few days.