Estimated to be at least the second-longest cave system in the country at 12.5km (it still hasn’t been explored to its terminus), Odessa-Tumbali Cave is for advanced cavers only. It can only be visited with permission from the tourist office in Tuguegarao and you must be accompanied by guide. Access requires a 7km hike from Callao Cave, followed by a 30m rappel into a sinkhole.
Lonely Planet's must-see attractions
The most accessible part of the area's immense 25km limestone cave complex is the seven-chambered Callao Cave. The cave is reached by 184 slippery steps…