Boston keeps an entire archipelago hiding in plain sight. The Harbor Islands — more than 30 of them, managed as a national and state park — sit a short ferry ride from Long Wharf, and stepping off the boat feels like leaving the city entirely. Civil War forts, swimmable beaches, hiking trails, skyline views: pick your island accordingly.

Georges Island and Fort Warren

More than 30 islands and peninsulas make up the park, but two of them do most of the entertaining. Georges Island is the classic first trip: the ferry pulls away from Long Wharf with the skyline unspooling behind you, and lands at the foot of Fort Warren, a massive granite fort from the Civil War era. You can wander its dark tunnels and grassy ramparts more or less freely; ranger programs fill in the history, including the fort’s years holding Confederate prisoners. Kids treat the whole island as a fortress-shaped playground, which is roughly correct.

Spectacle Island’s beach and summit

Spectacle Island is the harbor’s great comeback story: a former landfill rebuilt into rolling green hills, a swimmable beach near the dock, and trails climbing to the top of its drumlin — where the payoff is a full-width panorama of the downtown skyline across the water. It is one of the best views in Boston, and you earn it with a very modest walk. Smaller islands like Lovells, Peddocks, and Bumpkin go quieter and more rustic, with meadows, ruins, and in-season camping for those who plan ahead.

Plan like a sailor

The islands ask for a little seamanship. Ferries run seasonally — roughly May into October — and schedules vary by island and by day, so check before you commit. Services out there are thin: pack water, food, and sunscreen, because some islands have little more than a dock and a view. Glance at the forecast, since conditions on the water change faster than they do downtown. And know when the last ferry leaves your island. That boat is not a suggestion.