Hays Nature Preserve gives Huntsville a broad, easy outdoor space along the Flint River, with wetlands, woods, open fields, and greenway paths. It is a good counterweight to the city's space-and-engineering sights, especially if you want birds, shade, and room to walk.
The preserve is best in mild weather or early in the day during summer. Bring binoculars if you have them; the slower you move here, the more the place shifts from simple parkland to a useful little wildlife refuge.