Key largo-there are two state parks that are pretty dope, and you can also get a taste of the Everglades on an airboat tour out of key largo.
Islamorada-tons of water tours and activities to do. Pretty chill all around.
Marathon-half way point, haven’t spent much time there so I can’t recommend anything
Lower keys-More nature preserves/state parks
Key West-The Conch Republic BABAY!!!!!! So much history there. Recommended first stop Fort East Martello Museum. Logistically it makes sense to be your first stop. It’s right by the airport. It’s an old haunted civil war fort that also happens to house ‘Robert the Doll’. If you take his picture, ASK PERMISSION FIRST! Moving right along, Hemingway house. Ernest Hemingway lived in Key West for about 10 years. His residence is open to the public to tour, if you have any interest in the man and his incredible life make sure to stop by. There is also an old lighthouse up the road from his place that is pretty cool as well. Blue heaven, this is the best goddamn breakfast spot in America. If you like lobster, get the BLT benny. It’s orgasmic. And the ambiance of the place is so cool. Get there early! There are also some decent ghost tours if you’re into that, I enjoy that shit so YMMV. Duval street, it’s nothing but bars, restaurants, and shops. You can walk from one end to the other in about 20 minutes. It’s like nowhere else. I don’t know if you’ll want to spend a whole day going to see it, but it is amazeballs the Dry Tortugas is an old civil war fort built just in time to see the end of the war lol. It’s an incredible structure considering the time it was built, breathtaking really. But like I said, it’s an all day thing as it’s about 60 miles west of key west. Oh and don’t forget to stop by Kermits for some key lime pie brosef.