The Puerto Princesa Subterranean River National Park is a protected area in the Philippines. The park is located in the Saint Paul Mountain Range on the western coast of the island of Palawan, about 80 kilometers north of the city of Puerto Princesa, and contains the Puerto Princesa Subterranean River (also known as the Puerto Princesa Underground River). It has been managed by the Puerto Princesa city government since 1992.

The park has a limestone karst mountain landscape. St. Pauls’s Underground River Cave is more than 24 kilometers long and contains an 8.2-kilometer-long underground section of the Cabayugan River. The river winds through the cave before flowing directly into the South China Sea and is navigable by boat up to 4.3 kilometers from the sea.

The cave includes major formations of stalactites and stalagmites, and several large chambers, including the 360-meter-long Italian’s Chamber with approximately 2.5 million square meters volume. It is one of the largest cave rooms in the world. The lower portion of the river up to six kilometers from the sea is subject to tidal influences. Until the 2007 discovery of an underground river in Mexico’s Yucatán Peninsula, the Puerto Princesa Subterranean River was reputed to be the world’s longest underground river.

The 8.2-kilometer-long underground river boasts jaw-dropping cave formations, stunning limestone cliffs, and pristine waters, however, only a portion of the river, around 4.3km, is allowed for tourist explorations.

In 2010, a group of environmentalists and geologists discovered that the underground river has a second floor, which means that there are small waterfalls inside the cave. They also found a cave dome measuring 300 m above the underground river, rock formations, large bats, a deep water hole in the river, more river channels, and another deep cave, as well as marine creatures and more. Deeper areas of the underground river are almost impossible to explore due to oxygen deprivation.

The best time to visit Puerto Princesa is during its dry periods, which is from November to May. The warmest months are from March to May, while its wet season is from June to October. On June 30, 2019, Puerto Princesa underground river was celebrated with a Google Doodle.

According to Wikipedia