Although I have been to San Juan I have never made it to a beach there. There are none that I have seen coming and going from around the Point that I would call near the Port. I have however always just walked away to the left from the Docks and uphill then finding active squares and activities. However the latest I have been there was 2018 and was after a hurricane and things may have changed even more after covid. Hopefully someone thats been there recently can help. Getting to the Fort is walkable if you have good legs.. Just check google maps This "old guy" would not be doing that now days.