The Puerto-Princesa Subterranean River National Park features a spectacular limestone or karst landscape. It contains an 8.2 km long underground river that flows directly to the sea. The lower half of the river is brackish and subject to ocean tide. The associated tidal influence on the river makes this a significant natural phenomenon. The also contains a full mountain-to-sea ecosystem, and protects the most significant forest area within the Palawan Biogeographic Province. The conservation significance of Park’s forest at the international level is heightened when considered in the context of the high levels of past and current deforestation in the Philippines and in the region. The role of the Park takes a special urgency in this perspective. The conservation value of the Park is confirmed by the international recognition it has received.