Beautiful... you arrive by ferry (or seaplane) from Key West and suddenly see this red-brick fort seemingly out in the middle of nowhere. There are frigate birds, gulls, sooty terns, and pelicans all around - and endless sights of brilliant blue water.
Shortly after you arrive (10 to 10:30am) there is a guided tour of the fort. The guide tells you the history - and WHY there is a fort in this particular out of the way place. One wonders to themselves what it must have been like when there were 2,000 people living on this little spit of land (Garden Key is SMALL - the fort takes up most of the land area).
After the tour there is a buffet lunch for ferry guests - seaplane guests have a packed lunch. Then, many folks go snorkeling to see an array of coral and multicolored fish literally using every color in those 64 crayon packs, I think... Those who prefer to stay dry often walk around the moat, as by looking down from it, one can also see some coral and fish - many times starfish and other such creatures as well.
Later in the afternoon there is sometimes an additional tour - ours was up into the Harbor Lighthouse. There is a small gift shop for postcards, books, and other small souvenirs. Then, for daytrippers, it's time to leave (about 2:30pm). For those who are more adventurous, check on camping there (see my camping entry in this journal).