I see that Charleston, Savanah and Brunswick have all been mentioned. X2 to all of those. James Island County Park, Skidaway State Park and Blythe Island Regional Park are all favorites of mine.
However, within your parameters, my choice would be
Magnolia Branch Wildlife Reserve . Itโs operated by the Poarch Band of Creek Indians. Not your typical shuffleboard and bingo RV resort park but if youโd like hiking, fishing, kayaking, tubing, zip line and general back to nature, itโs a great choice.
(Nearby casino too, if youโre into that.)
Larry