A small sidetrack from the jungle paths leads to El Dorado Cavern, which possesses a unique limestone formation, testament to the immensely ancient geological forces that shaped the Peninsula. At one time in its history, the whole of the Yucatan Peninsula was thought to be coral formations, completely submerged in the sea.

El Dorado supports this theory, its walls being studded with fossils of ancient mollusks and other prehistoric specimens. A beautiful blue-green pool lies underfoot, hinting through the minimal crack towards the abyss, at the interconnection of underground waterways underlie Xel-Ha.