Here is the BBC program "Secrets of the Maya Underworld"- Deep Beneath the Yucatan Peninsula is a vast network of Cenotes connected through underground passages, underground caves and underground flowing rivers. It is no wonder the Mayans believed the Cenotes to be the Gates to the Underworld. Some of the Cenotes are indeed truly beautiful and breathtaking. Deep in the Underworld modern researchers have even found the bones of Mammoths that went extinct 10,000 years ago. Modern science has not even begun to discover or comprehend the full implications of the secrets which lie beneath the Maya Underworld. Articles- http://travel.nytimes.com/2007/02/23/travel/escapes/23Cave.html http://yucatantoday.com/en/topics/caves-yucatan