The second-longest of the many bridges that make up US-1, the elegant multiarched Long Key Bridge supports a long flat causeway where the road finally earns its other name, the Overseas Highway. Unobstructed views of the distant horizon are yours in all directions, with the narrow ribbon of highway seemingly suspended between the sky and the sea. Fortunately, turnouts at both ends of the causeway let you take in the vista without worrying about oncoming traffic.

The Long Key Bridge marks the northern end of Marathon, a sprawling community that’s the second largest in the keys, stretching between mile markers 60 and 47 over a series of islands. One of the visitor highlights of Marathon is on Grassy Key, where the Dolphin Research Center (MM 59, 305/289-0002, daily, $28 adults), a rescue and education facility for the study and care of marine mammals, is marked by a 30-foot-tall statue of a dolphin mother and baby. You can swim with a dolphin for around $199.

Accessible by ferry from a visitors center in Marathon, Pigeon Key (MM 47, 305/743-5999, daily, $12 adults) is one of the least famous but perhaps most fascinating spots along the Overseas Highway. A national historic district, preserving substantial remnants of the clapboard construction camp that housed some 400 workers employed on the original Seven Mile Bridge from 1912 to 1935, Pigeon Key offers a glimpse of blue-collar keys history the likes of which you’ll find nowhere else.