Vitamin D -- specifically the form D3 -- is the only vitamin your body makes itself. It's fat-soluble, which means your body stores vitamin D in its adipose tissue -- in its fat. And, if you want to be specific about things, this vitamin is actually a hormone.
Sullivan's Castle Island, South Boston, MA, Est. 1951. Castle Island. Located at the end of Carson Beach, on Pleasure Bay in South Boston, Castle Island is a 22-acre recreation site, and the site of Fort Independence. Castle Island was really an island until several land reclamations through the years extended causeways and eventually roadways.
3 to JFK Exit, follow beach along William J. Day Boulevard, Castle Island is at the end of the Causeway. MBTA: Castle Island, M St. Beach - Red Line to Broadway Station, then take City Point buses #9 or #11. Walk to the right across Marine Park to the beach to the entrance of the fort.