Seven Mile Bridge, Road bridge between Marathon and Little Duck Key, Florida Keys, US

Seven Mile Bridge is a road viaduct linking Marathon to Little Duck Key in the Florida Keys. The structure rises about 65 feet above sea level and rests on hundreds of concrete piers stretching nearly 11 kilometers through shallow bays and sandy channels.

The first crossing was built between 1909 and 1912 as a railway line connecting Key West to the mainland. After severe hurricanes in the 1930s damaged the original route, it was converted for automobiles until the current concrete bridge was completed in 1982.

The name refers to the length of the crossing over open water, which drivers follow from the middle part of the island chain to the next inhabited island. Anglers and cyclists use sections of the old viaduct alongside as a public path with views of the shallow bays and reefs around.

The route runs in a straight line from one island to the next and can be challenging during strong winds or rain because there are no protective windbreaks. Sun protection and plenty of drinking water are advisable, as the roadway sits fully exposed above open water.

Pipes beneath the roadway carry freshwater to the southern islands because they lack their own groundwater supply. Crossing the span means also traveling above one of the longest freshwater pipelines in the entire Florida Keys.