Monserrate Balneario Beach in Luquillo
In Puerto Rico, balnearios are public beaches which are run by the Puerto Rican government. Unlike other beaches, these beaches cost money to get into (unless you sneak in). Usually the price is about $3-$5 and for the money you get a cleaner beach than others...for the most part. There are life guards on duty on this beach but the waves are generally pretty calm due to the reefs which slow down the waves prior to reaching the shore. There are public bathrooms and plenty of parking nearby. If you get hungry, the kioskos are within walking distance.
If you want to camp at this beach you can rent a spot for $10 per day.
Administration Office of the Balneario La Monserrate: 787-889-5871
Puerto Rico Tourism Company: 787-721-2400