I managed to find a trail at Biscayne National Park. I spent my entire time on the Spite Highway, a seven mile trail that bisects Elliott Key. Yes I ran it back and forth around 3.5 times. There isn't much land associated with Biscayne National Park. Most of it is protected marine areas.
I had to hire a boat to take me the 45 minutes from Homestead, FL to the key. I camped for a night right near the dock.
If you want to learn why it is called the Spite Highway you can listen to the longest narration about a park I did while running during the entire project. I guess I thought it was interesting and I had no one else to talk to.
While I don't mention it during the run there were tons of spiders and spiderwebs crossing the trail. The first pass in either direction I ran with a stick in my hand to break down the webs before they ended up in my mouth, stuck to my shirt or in my eyes.
While somewhat repetitive it was a fun run through the shade of the foliage which has reclaimed the Spite Highway.