"Fort Jefferson takes up 90 percent of Garden Key. It has a huge feeling of history, and you get the feeling that it wasn't an entirely happy history. You can tell that there was a lot of blood and sweat that went into constructing this.
"The park department has tours you can take, but you don't even really need to listen to them to get a sense of the immensity and probably the sacrifice that was required to build this in such a remote and hot, muggy place."
Photographer Tim Calver