Progreso beaches are not the white sand that most are used to. The shore is lined with sea shells. I would suggest water shoes. I didn't go in but walked the beach and many people were enjoying it. This was a short walk from where the shuttle drops you off. AutoProgreso runs the free shuttle from the ship (the pier is 4.6 miles long). Once you get off you walk past the market then turn left - keep walking until you hit the beach.
You said you didn't want to pay - but AutoProgeso does offer the same beach break as Carnival but much cheaper. It's a 4 or 5 star resort and includes snacks and drinks. We didn't do it this last time but may try it this next time. You can find it on their website at www.autoprogreso.com - It's listed as Open Bar.
Hope 2 Sea U Onboard - Cheryl

Fantasy, Inspiration (2), Conquest (2), Spirit, Ecstasy (2)
Coming up: Triumph (November 28, 2009 - Penthouse - Sweet!)