Biscayne is the national park Miami forgets it has, and the reason is simple arithmetic. Around 95 percent of it is water. Drive to the Dante Fascell Visitor Center at Convoy Point in Homestead, walk the short boardwalk, look out at a flat green bay, and it is entirely possible to leave thinking you have seen it. You have seen the car park.
The park protects four connected systems stacked one behind the other. First the mangrove shoreline, the longest undeveloped stretch left on Florida's east coast. Then Biscayne Bay itself, shallow and clear-ish and full of juvenile fish that use it as a nursery. Then a chain of low coral-limestone islands — Elliott Key, Boca Chita, Adams Key — which are the northernmost Florida Keys, reachable only by boat. And beyond them, the northern end of the Florida Reef, the only living barrier coral reef in the continental United States.
Getting onto the water is therefore not an optional extra. It is the visit. Boat trips run from Convoy Point through the park's non-profit partner and through permitted operators: snorkel and dive trips out to the reef, sailing afternoons, paddling in the mangrove creeks near the visitor centre, and heritage cruises past Stiltsville — the cluster of wooden houses standing on pilings in open water off Key Biscayne, built from the 1930s onwards, now inside the park boundary and preserved as a curiosity of Miami's more inventive decades.
Underwater, the park runs a Maritime Heritage Trail: a set of buoyed shipwreck sites from a nineteenth-century wooden hull to a steel steamship, most of them requiring a boat and several requiring dive skills. It is the only trail of its kind in the national park system.
There is no entrance fee. The park is free to enter, which is unusual and worth saying plainly. What costs money is the boat, and without one you are looking at a very nice view of somewhere you did not go.