Have you been to Mambuaya Cave (formerly Monigue Cave) located in Brgy. Mambuaya, Cagayan de Oro City, some 20 kilometers southwest of the city proper?
As stated in a Tourism Marker onsite, the cave with a total length of 438.4 meters was declared an Adventure Destination way back in 2005. But because primarily of its distance and undeveloped access roads, the cave is less visited by tourists but is a favorite among spelunking enthusiasts. What makes this cave distinct is its small entrance where the only way to get inside is to go underwater. Another natural attraction are the crystal-like formations of stalactites and stalagmites where the only light source is the waterproof headlight you will carry.
See this video courtesy of The Weekend Breaks which basically gives you a step-by-step guide.