On a budget, Boston Harbor Islands still earns its price.
Ferry ~$25 round trip
An underrated escape — a short ferry lands you on quiet islands with hiking, swimming, harbor views, and the genuinely spooky tunnels of Fort Warren on Georges Island. The catch: it's a committed half-to-full day around ferry schedules, amenities are sparse (pack food and water), and it's weather- and season-dependent (mostly May-October).