While the subterranean river is actually over 8km in length, tourist paddle boats are allowed to go only 1.5km upstream into the cave (45 minutes return). It’s possible to proceed 4.3km upstream with a permit from the Subterranean River National Park Office in Puerto Princesa (P1000, four hours return), secured at least two days in advance. The limestone cave that the river passes through is one of the longest navigable river-traversed tunnels in the world.
Along the way, your guide, with the help of a spotlight, will point out various features of the caves (this usually means one-liners and double entendres like ‘we call that formation Sharon Stone’ rather than geological facts). When looking up, keep your mouth shut: bats and swiftlets flutter above and are responsible for the guano that ‘perfumes’ the cave. In 2010 a team of Italian spelunkers discovered the million-year-old fossilised remains of a dugong (sea cow) on a part of the cave wall not currently open to the public.
Once in Sabang, the Sabang Information Office at the pier can arrange boat transport (round trip for six people P700, 15 minutes) and process your environmental fee. The boat from Sabang pier drops you off on a beach near the entrance to the cave (a few crab-eating monkeys and monitor lizards roam the area); from there you walk five minutes to the actual entrance and are assigned a boat for the trip into the cave. Alternatively, you can also walk 5km to the cave from Sabang via the 'jungle trail' (entrance P200).
Important note: if travelling independently, you must secure your park permit in advance from a tour operator or the national park office in Puerto Princesa. However, if you are sleeping in Sabang, or if you are coming direct from El Nido or points north, you can purchase your permit on-the-spot in Sabang provided you can show an accommodation receipt.
Of course you can also visit the park on an all-inclusive tour out of Puerto Princesa (P1500 including transportation, lunch and all fees), Unless you are pressed for time, we don't recommend these as they herd you in and out of the park and preclude you from exploring Sabang's rich coastal rainforest.
Officials often close the park due to excessive rain or rough seas, so when there’s inclement weather we suggest contacting the Sabang Information Office in advance to save you a disappointing trip out to the river.
Read more: http://www.lonelyplanet.com/philippines/palawan/sabang/activities/boating-cruises/puerto-princesa-subterranean-river-national-park#ixzz3zV89rMWI