It is $5/car entry fee at the gate at St. Marks NWR. There is a Visitor Center to the right just after you go through the gate. We drove straight to the Lighthouse which is literally at the end of the NWR road. It is not a short road either. You can easily envision it being the same road that was there in wartime too. Nothing but flooded timber,coastal marsh, marsh ponds and small canals on either side of the road as far as the eye can see. Couldn't see anywhere else where a road mighta been. At intervals,there are areas to launch canoes, kayaks and trolling motor powered boats.There are fishing and picnic areas and some hiking trails too.
In Dale Cox's book,he wrote that the Union troops brought artillery but no artillery horses. The cannons had to be manhandled to the areas they were used. I'm guessing powder,ammo and other supplies had to be moved the same way. Most of the Union troops in the Natural Bridge Campaign were USCTs. They earned their $10 in March 1865.