Before tree huggers and other nature lovers quashed plans for an overseas highway down the center of Elliott Key in the late Sixties, developers bulldozed a six-lane-wide opening. When the dust settled, the key emerged as part of Biscayne National Monument, which Congress reclassified as a national park in 1980. In the years since, managers of this offshore Eden have allowed the foliage to reclaim all but one unpaved lane, which now forms a seven-mile trail. There's also a one-mile loop that slices through the hammock and turns into a boardwalk with an ocean view. If you take either path between April and June, try to spy an endangered Schaus's swallowtail butterfly along with the usual herons, egrets, warblers, and hawks. Or bring your snorkel and check out the rays, sea grass, and sea cucumbers. The best way to get to Elliot Key, unfortunately, is by private boat. The park service's boat concessionaire will take you roundtrip from the Convoy Point Visitor Center on SW 328th Street and Biscayne Bay for $21 per person, but only if you stay overnight and make reservations well in advance. Park authorities recommend avoiding the island during the summer because of mosquitoes and other insects.