The van ride from Puerto Princesa to the Palawan Underground River in Sabang is a 2 to 2 1/2 hour trip with several scenic views.
Limestone cliffs
The van ride ends at Sabang wharf where the tourists get their permits and the corresponding boat ride to the underground river.
Sabang wharf
*Please get your permits in advance as during peak season(e.g summer). There's usually a number of permits alloted for walk in guests, but there is a risk you won't get a permit if the daily allocation runs out.
It takes around 30 minutes to get to the actual Underground river which offers more spectacular views.
Cave entrance
Note that visitors will likely get wet during this tour as water is dripping from the cave. Plus, all visitors are required to wear life vests and hard hats as bat guano and other animal droppings may fall from the cave ceiling.
This is one reason I could not take a lot of photos while inside the cave. An water proof or underwater camera may be used but the place is also extremely dark as each boat only has one light held by the passenger in front (or the ship's bow). I took photos with my waterproof Point n Shoot instead of my DSLR, but they were not that good as the latter's flash and AutoFocus were weak. The cave is really cavernous with the camera's flash barely reaching the walls and ceilings.
The actual cave tour lasts around 45 minutes. Your tour guide and boatman may allow you to spend a few minutes observing or taking photos of the 'inhabitants' of the forest surrounding the river.
Note that these animals are not caged and roam the park freely. Though these animals are already used to seeing a lot of humans, it is still a good idea to exercise proper caution when dealing with these wild animals. (translation: don't get too close, the monkeys get aggressive thinking that the tourists have food)
Varanus monitor lizard (bayawak)