Explore the hidden chambers and crystalline waters of the mayan underworld at actun tunichil muknal atm featured in national geographic swim into the mysterious cave which the ancient mayas considered to be a portal to the underworld known as xibalba this day trip from san ignacio includes a 15 hour round trip hike in tapir nature reserve and lunch at the cave entrance climb crawl swim and play in the water passage as you enter the caverns and delight in the refreshing waters of the