Bahia Honda means deep bay, and the name is a clue to what makes this island special. Most of the Florida Keys are flat, fringed with mangroves and shallow, but here the water is deep enough close to shore that Henry Flagler's railway engineers had to build a long steel truss bridge to cross the channel. That bridge, completed in 1912 as part of the Overseas Railroad, carried trains to Key West until a hurricane in 1935 destroyed much of the line. The railroad's bridges were then converted for road traffic, and the old steel structure at Bahia Honda, with its girders overhead, was used by cars until the 1970s. Part of it now stands unused as a lookout, cut short in places, a rusty ghost above the water.
The state park here has some of the best beaches in the Keys, with pale sand, clear water and tropical vegetation. The sea is the colour of turquoise, and you can walk in warm, shallow water for a long way. Snorkelling off the beach is good, and the park is a refuge for plants and birds found nowhere else in Florida. In the evening, the sunsets over the Gulf are glorious. The park charges an entry fee, and motorcycles pay a small amount.
The Overseas Highway, US 1, runs for 113 miles from Key Largo to Key West, over dozens of islands and forty-odd bridges, and it is one of the world's great road trips. The riding is easy rather than technical, with flat, straight roads and the sea on both sides. Speed limits are strictly enforced, and the traffic can be heavy, especially on weekends and holidays. Watch for the tiny Key deer, an endangered subspecies found on Big Pine Key, close to here, and obey the lower limits at night.
Fuel is available at Big Pine Key and Marathon, and again at many places on the route, though prices are higher than on the mainland. Heat and humidity are fierce in summer, and afternoon thunderstorms arrive fast. Winter is the best season, when the air is warm and dry. Take sunscreen, water and a light rain jacket, and make time to swim.