Pigeon Key is a tiny island under the old Seven Mile Bridge, once a work camp for the men building the Overseas Railroad. Restored buildings now hold exhibits on the railway, the bridge, and the brutal labour of building across open water in heat, storms, and isolation.
It is one of the best places in the Keys to make the Flagler railroad story concrete. Go when tours are running, and combine it with a walk or bike ride on the old bridge approach from Marathon.