The Underground River is located at the base of the karst limestone St. Paul mountain range. Through the ages, rainwater seeped into its cracks and crevices, creating water passages and tunnels. The tides coming from the sea also affects the ebb and flow of the water into the Underground River, slowly carving some walls of the cave. Underground River is the most popular attraction in Palawan. Having been named as one of the New 7 Wonders of the World, it is also one of the Philippines’ top tourists attraction.