What are the best things to do in Key West/Miami?

Me and my husband are going there this coming week and we are staying in Naples for his cousin's grad. But we have one day to explore South FL and I wanted to do the best things in a short amount of time.Any ideas? Even off the beaten path?What are the best things to do in Key West/Miami?
If you like outdoor stuff try:

Kayaking at oleta state river park in north miami.

Bayside marketplace in downtown miami: you can eat, shop and go on boat tours of star island.

airboat tours in the everglades.

South beach has a few museums and attractions like the Versace house.

Key west has good jet skiing and conch.What are the best things to do in Key West/Miami?
I don't suggest airboats, althought their fun, I've heard people have gotten into accidents with the alligators and stuff..idk..

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