The beaches inside Fort Clinch State Park are the island's most interesting, because you get two of them with different characters plus a pier, and because they come attached to an 1847 fort.
They are inside the park, which means you pay the Florida State Parks per-vehicle entry fee to reach them and you arrive down a mile of road under live oak canopy. Both facts change the experience relative to a roadside access.
Two beaches
The ocean beach on the park's east side is proper Atlantic surf: wide, firm, exposed, with the same grey-gold sand as the rest of the island. It is backed by dune and boardwalk, and it is quieter than the city accesses simply because fewer people pay to get in.
The river beach on the north side, near the jetties, faces into Cumberland Sound rather than the open ocean. The water is calmer, the slope is gentler, and it is the better choice with small children. The view across the sound is of Cumberland Island, Georgia — wild, undeveloped, and startlingly close.
The pier
The fishing pier at the park's northern point reaches out over moving water at the mouth of the sound, which is why it fishes well. A Florida saltwater fishing licence is required for most anglers; pier rules are posted.
Even if you do not fish, the pier is the best vantage point on the island for watching ships come and go — this is the entrance to a working port, and the traffic includes Navy submarines out of Kings Bay to the north.
Shark teeth and shelling
The jetty area and the north beach are the island's best-known spots for fossil shark teeth and shells, particularly after a blow when the surf has been rearranging the bottom. Low tide is the time to look.
Practicalities
Florida State Parks charges per vehicle to enter, and the fort has a small additional charge. Both are set by the state and change, so check the park's page rather than trusting a figure here. The park and the fort keep different hours and we have confirmed neither, so check the park's page rather than a figure here.
Facilities inside the park include restrooms near the beach areas and at the campgrounds. There is no concession stand of any consequence — bring food and water.
Dogs in Florida state parks are subject to rules that differ from city and county beaches and are usually more restrictive on the sand itself. Check Fort Clinch's own dog rules before arriving with a dog expecting a Main Beach experience.
Combine it with
The fort, obviously — half a day covers both. The park's six-mile off-road bike trail, and the shorter walking trails through maritime hammock. Old Town Fernandina is immediately outside the gate, and downtown is ten minutes away.