Just 30 minutes south of Cancun is a fishing village named Puerto Morelos. 
It is a quaint, true Mexican fishing village.  Puerto Morelos is somewhat of an anomaly in that it sits between Cancun and Playa del Carmen and yet has seen little growth.  It is literally like stepping back 50 years in time. Just recently have some big hotels begun to move into Puerto Morelos.
This is a great location to go snorkeling - as the reef is a quick boat ride away.  The reef is approximately 1 mile offshore so do not think you can get there by swimming.  It is too far. 
There are lots of good restaurants, private homes, Bed & Breakfasts, & Condos for rent and even a bookstore full of books in English. 
If you have a rental car Puerto Morelos is a great place to go for a few hours and relax, have lunch or dinner and enjoy the way Mexico was 50 years ago. 
Puerto Morelos also has a fishing tournament every May which is a nice event to go see as Blue Marlin, White Marlin, Mahi Mahi, (Dorados) and others are caught and exhibited.
The church is small and pretty and is a great way to get a true taste of the community.  Be sure to check out Puerto Morelos!