Discover rio secreto a stunning underground river and semi sunken cave system with thousands of dramatic stalactites and stalagmites explore the captivating subterranean world where the history of our planet is written on the myriad rock formations itinerary rio secreto is a journey through an underground river in the riviera maya whose intricate rock formations and crystalline water tell us more about the geological history of the region it is the largest partially flooded cave in the ar