Like so many of the cities and islands of the Florida Keys, Marathon is a laid-back, almost tropical destination. In 1909, the Seven-Mile Bridge was constructed, and it remains an engineering wonder today. An annual foot race takes place across the bridge, bringing with it competitors from all over the world. For an up-close look at marine animals, a trip to the Dolphin Research Center is in order. Families of dolphins and California sea lions reside here. With its ocean location, Marathon is also a popular place for scuba diving and numerous boat tours.