Cayo's Mountain Cow Cave, located in the Blue Hole National Park, was on Overlander TV. They went with Hun Chi'ik Tours. This is a great video of one of Cayo's best caves.
"We start the tour by hiking through the steamy jungle, I film my first Blue Morpho Butterfly. We then descend into the Mayan Underworld, going 150 metres down into the cave system, that has been used for ceremony since ancient times. Maya shamans and priests would enter into trance in crystal cave to conduct their ceremonies and rituals. We see huge caverns adorned with spelothems and crystalline formation, artifacts of pottery, beads, obsidian blades and human skeletal remains that have been calcified in the limestone floor. Crystal Cave is located in the Blue Hole National Park. After exploring the realms of the Under world (xibalba), we hike back to the vehicle and drive for five minutes to the Blue Hole for a refreshing swim."