The Island Province of Palawan, often called the Philippines’ last frontier, has a unique concentration of UNESCO coastal and small island initiatives. In 1992 UNESCO classified the entire province as a Man and Biosphere Reserve. The island’s Tubbataha Reef Marine National Park is a World Heritage Site, as is the Puerto-Princesa Subterranean River National Park, with the world’s longest underground river (8 kilometers). source: http://www.unesco.org/csi/act/ulugan/ulugan1e.htm
My Palawan Adventures starts with Puerto Princesa. We all know what comes next, The Subterranean River National Park - The Underground River.
Palawan’s prime tourist attraction, the Puerto-Princesa underground river. Again, uncontrolled tourism would quickly wreak havoc, as it has elsewhere. - UNESCO
Also here's another post about taking care of the Underground River #Let The River Rest