Castle Island is not really an Island any more, but it’s still in Boston Harbor, part of the Boston Harbor Walk. It’s a fun beach + fort + other stuff combination. We went last weekend with Alli and her parents, and had a great time.
The beach is really close to the city, in South Boston, an easy drive.
Parking was relatively easy, not in the main beach parking lot (too small), but along the road leading to the beach. Thankfully there is beach along much of the road, and a nice walking path the whole length.
The fort, Fort Indepenence, is cool. We walked around it, noted the cannons, read the history, etc. Not your usual beach. The beach itself is not bad. The water was a bit cold, and the sand is not amazing, but it’s not bad.