Ben Franklin Drive goes all the way to the south end of Lido Key, and ends at the parking lot of South Lido Park. Admission is free, and parking is free. On the way to the park you'll pass big hotels like the Harley Sandcastle. South Lido has several nice hotels right on the beach.
At the park there are lots of picnic tables, playground equipment for the kids, decent bathrooms, and picnic tables on the bay side, and overlooking Big Pass. Water currents are very strong here and I would not advise swimming. However, you will see some people venture into the water. There are NO lifeguards at this beach.It's nice for having picnics, letting the kids run around and play, sunbathing, and just enjoying the view of Big Pass and northern Siesta Key across the way.