The many pleasures of beautiful Cancun cause most to overlook the El Rey Ruins, a collection of 47 ancient structures strung along 550 meters in the jungle between beach and golf course on the southern end of Cancun. A hike, bike trip or taxi will take you to the entrance at N 21 03.559 W 086 46.891. Entrance to the area is 27 pesos (about $3, the best deal in Cancun, and it is free on Sundays!). A new entrance is being built as of April 2002. Tours are available, or you may self-guide a walk back into history. Unlike many other ruins, you can climb these for views and photos.
The settlements date to 1200 A.D., not as old as other, more famous ruins, but no others are a better kept secret. The civic-ceremonial area is marked by coliseum-type structures and a twenty foot tower which still holds two altars at the top of what was a temple. Here is where El Rey (The King) surveyed his community.
From the temple overlook, look back toward the park entrance; toward the beach, at your 10 o'clock position, look 120 feet toward a clump of dense vegetation. It is also some 50 feet (18 paces) southeast from the base of the tower. On the beach (east) side, look into the vegetation, and the cache will be a Rubbermaid container within arm's reach.
P.S. Pay no mind to iguanas. They will move out of the way!