That's the main entrance. It's the best supply port in the Keys, with easy access to things like groceries, a Kmart, auto parts, a West Marine, lots of smallish marine businesses, etc. If you need to work on your boat it's the best spot in the keys, and there is every usual service ashore. Lots of people apparently like to just hang out in one place and don't want to deal with anchoring, so the mooring field is very popular. We spent some weeks there once installing new self-steering, and gearing up for two years outside of the USA. It was much more pleasant doing it there than in a lot of Florida, and we could take day trips out to the reefs, or dinghy down Sisters Creek to the beach. In the winter it is much more sheltered than most harbors, and when you have cold fronts coming through with 40 knots from almost any direction it is nice to have 360 degrees of protection, which you don't in most Keys harbors. Key West is just nasty in a norther. The cruising community is friendly. I would not rate it as "must see," but for what it is good for it is pretty good.