The has a list of their beaches with individual facilities on their website. Look for "ducha" (shower) in the facilities list.
One of the beaches I have visited is Cerro Gordo Beach in Vega Alta. You pay a few bucks to have secured parking. It's a beautiful beach with a huge area to choose from, including many tall Palm trees that provide shade if needed. Depending on the season, they will also have food trucks set up. Last time we went there were 4 to choose from, including a soft serve ice cream truck. You can also bring a grill if you are so inclined. I've never seen a beach where there wasn't a grill though.
There are few places in the surrounding area to explore and they even have a MTB trail.