There’s not much to see at the Southernmost Point Buoy (South St. and Whitehead St., a block east of Duval St.) other than, well, the buoy. That buoy—brightly painted in black, red, and yellow—is close to the heart of historic Key West [1], and nearly all visitors make their way here for a snapshot, as it notes the fact that you’re not only at the southernmost point in the continental United States, but also only 90 miles from Cuba [2].
Although there is almost always a small crowd of people nearby waiting their turn to take a photo, you’ll be in and out, photo in hand, in less than five minutes.
Links:
[1] http://www.moon.com/destinations/florida/florida-keys/key-west
[2] http://www.moon.com/destinations/cuba