Film about the Mayan underground world

Dear sir/madam. Some years ago I watched an interesting film. There was shown a documentary movie in which some people were studying the karst system in Yucatan. Within the furthest and the deepest of the cave they found a small entrance completely blocked with stone (which seemed to be made by human hands as it looked very elaborate like a stone wall from a masonry), which was supposed to lead into the Mayan underground world (or a kind of a temple). This entrance was supposedly blocked by the Mayan priests, in order to keep the Spanish out of the sacred place, when the latter invaded their lands. The scientists left the entrance as it was, and there the movie came to an end. And I failed to find any further information about what happened after. If you have any, please let me know what kind of cave it finally turned out to be and what kind of movie was it? Thanks beforehand.