In the 1960s the Aerojet company was considered* as the possible supplier of solid-fuel rocket motors to be used as primary power plants for the Saturn I space booster. The idea was to use a single, very large rocket motor in place of a cluster of smaller, though still large motors on the Saturn’s first stage.
The first-stage motor (see also the photo of a test-firing on this page) was to be approximately 21 feet in diameter — so big that it could not be transported by road, rail or air. Aerojet therefore built a facility in the Florida Everglades, about forty miles South-Southwest of Miami and remote from residential areas, where the motors could be assembled and tested, and from there barged to the Atlantic Ocean and then up the coast to Cape Canaveral, where they launched the rockets. The State of Florida provided land and built the canal that Aerojet wanted. (A corporate-welfare boondoggle, yes, but probably a modest one in the grand scheme of such things.)
[*Update: Rand Simberg was kind enough to link to this post. One of his commenters says that Werner Von Braun, designer of the Saturn I, never considered using a solid booster, and that Aerojet’s Everglades plant was thus a self-inflicted boondoggle by the company. Another commenter provides a link to a website (search on the word “Thiokol”) that provides information about a plant that Thiokol built in Georgia to develop rocket motors similar to the ones that Aerojet developed. At least one of the Encyclopedia Astronautica articles about Aerojet, to which I linked above, mentions Thiokol as a parallel developer of large solids. However, I don’t know enough to evaluate this information, so I am putting it all out with the suggestion that you read the comments on Rand’s post.]
You can read the Encyclopedia Astronautica articles linked above to get a better idea of the project’s technical history. The short version is that NASA never did use Aerojet’s giant rocket motors, and Aerojet eventually gave up on its plant and sold the land back (nice trick) to the State of Florida, which holds it to this day as a nature preserve. Most of the original buildings associated with the plant, and some of the machinery, appear to be still there, albeit in decrepit condition. It’s accessible, though the last couple of miles of the access road are closed to motor vehicles, so if you want to visit you have to bicycle or walk part of the way. There are a few houses nearby, and people come to bird watch or to fish in the canal that parallels the road, but the place is essentially deserted once you get past the no-motor-vehicles-beyond-this-point sign.