I encountered this big guy in a park in Pinellas County, Florida back in April. Butch Norden has identified it as a Gopher Tortoise (Gopherus polyphemus). This species, a native of southeastern U.S., is generally threatened throughout its range, probably mostly due to habitat loss to development.
Here is a close-up of the head. I noticed later while looking at the fully enlarged pictures on the monitor that there is something stuck under its eye. I don't know what it is, but it doesn't quite look like a tick (here is a turtle with a tick).