Workers stayed on this island for decades building the Flagler Railroad. The headquarters of the project was held here at historic Pigeon Key. You can tour it and learn all sorts of fantastic tidbits of information on how it was back then. A really low cost boat ride is offer from the Knights Key Chamber Office, at the base of the Seven Mile Bridge on the Marathon side of the bridge. You can walk the old bridge all the way out to see it first hand or take the boat ride!
When you walk out on the bridge using the old bridge, look down and you can see sharks and critters swimming. Go when the winds are light and you really have the best of water clarity and sightseeing from the pier park.
The boat ride to Pigeon Key is really neat. You can walk it on the old bridge, which is about two miles out. Bicycles are legal to use to travel the old bridge, which then is only about ten minutes or so.