Nearly eleven kilometres of road laid across open water, with the Gulf of Mexico on one hand and the Atlantic on the other: the Seven Mile Bridge is the great set piece of the Florida Keys. The modern span opened in 1982 and rises in a gentle hump in the middle to clear boat traffic, and from the crest you can see the water turning from pale green to deep blue in bands, with the horizon curving slightly and the keys scattered like dark commas. Riding it is a short, strange, wonderful experience, a few minutes in which there is nothing but sky, sea and a ribbon of tarmac.
Next to it, running in parallel for most of the distance, is the old bridge, built by Henry Flagler's railroad in 1912 and later converted for cars. The Overseas Railroad was an astonishing piece of ambition, a line running from the mainland to Key West across the water, and it carried trains for twenty-three years until the Labor Day hurricane of 1935 wrecked the line. The roadbed and bridges were then bought by the state and turned into the Overseas Highway. The old span is now closed to traffic, though part of it can be walked or cycled out to tiny Pigeon Key, a former work camp that now has a small museum.
For a rider, the bridge demands respect for wind. A crosswind from the Gulf can push a bike sideways, and on bad days gusts make it feel as if the sea is leaning on you. The speed limit is low, around 55 mph, and the road has no shoulder worth the name, so any breakdown has to be pushed onto the tight edge. Watch for the odd heron, and for the sun at either end of the day, which can glare off the water. Summer storms build quickly over the Keys, and a squall in the middle of the bridge is not pleasant.
The nearest town of any size is Marathon, about eight kilometres to the northeast, with fuel, food and a handful of places selling fresh fish and the key lime pie that every restaurant in the islands claims to have invented. From there, the road continues south to Key West across a string of smaller bridges. Sunrise and sunset are the best times to see the bridge, when the light is softest and the traffic thinner. Take your time, and stop at the end for a look back, where you can see how thin the line of road really is.