The cache is located at the Florida Keys National Marine Sanctuary's Eco-Discovery Center. The Center is at the end of Southard Street, on the way to Ft. Zachary Historic Taylor State Park. Park for free in the Center's parking lot and notice the colorful wall. This is primarily a logbook cache but you may trade items if you wish. Occasionally there are trackable NOAA Geocoins.
Use this limerick to narrow your search:
Look all around for the very last post
Because it's the one that acts as the host.
The hidden cache holds tiny treasure
For an adventure that goes beyond measure
And once found leads to many a boast.