The Manacota Underground river is located in Marag Valley Luna, Apayao.
Upon going to the underground river, you need to pass through the Manacota River itself for like 30-mins to 1 hr.

And ofcourse you need to ride a boat upon entering the cave because the water is so deep. The cave is really cold, and you really need a lot of flashlights for you to be able to see it's beauty inside.

And as you can see the water is really clean. And because it's a running water, you might get taken away by it's currents so always be careful!