There aren’t too many places where you can do long bike ride and camping through tropical beach land paradise, but the Florida Keys happens to be one of those places. Here’s the skinny. It’s about 160 some odd miles, give or take between Miami and Key West. You can do the whole thing or you can do a halfway with a turn around, stopping somewhere in Islamorada, which is about the halfway spot. While the full oneway trip gives the anticipation of “getting to a finish line”, from a purely practical standpoint, you have to get your bike and gear back from whence you came. There are good little hotels pretty much all along US 1 so if you’re not in to camping you can easily find rooms, although you should reserve in advance, The Keys are always popular.
The ride is mostly flat, no hills. The traffic is easy going, once you’re on the overseas highway, it’s a two lane road and cars can’t go to fast, so it’s relatively safe. Good walkways and paths on all the islands.
If you can we would recommend you go sometime between December and March when it’s coolest and not middle of hurricane season. There are lots of great guides all around the web that have advice on where to stay and where to eat along the way.