Alfred B. Maclay State Park & Gardens
http://www.floridastateparks.org/maclaygardens/
Although I've never been to the recreational area of the park, I have visited the gardens and they are spectacular. During the winter, they look a bit shabby and udergroomed, but they are large and filled with a variety of gorgeous plants, winding brick trails and relaxing stopping points with chairs and benches. This is a popular spot for photography, but is great for gathering with friends, doing homework or just relaxing.
Some of the scenery at the Gardens: 1 2 3 4