Sunday we biked 25 miles on the southern end of the Withlacoochee State Trail, the longest paved trail in Florida at 46 miles, running south from Gulf Junction Trailhead to Trilby. We did the southern section, since it was right near our motel. A large trailhead lot is available just off Route 50 east of Brooksville about 10 miles (and east of I-75 about 1.5 miles) at Croom-Rital Road. I have done the northern section a few years back. The trail is 12 feet wide and in good repair.
This southern section runs along the river in places and much of the trail goes through the Withlachoochee State Forest as seen below. A mountain bike loop is available in the Groom area near where I-75 crosses the trail. Rest areas are available at regular intervals and trail access areas have washrooms and picnic tables. Since it is a rail-to-trail, it is basically flat.
A map is available here.