Tucked into the edge of South Boston on Castle Island, Fort Independence is easy to miss if you’re flying by on I-93 or Route 1. But if you swing down Day Boulevard and loop around the harbor, it’s hard to ignore—a massive stone fort perched on the water like it’s still guarding the city. And in some ways, it is. This spot has been fortified in one way or another since 1634, making it one of the oldest continuously fortified sites in the country.

Originally called Castle William, the fort changed hands with the tides of history. The British used it during the lead-up to the Revolutionary War, and when they fled Boston in 1776, they trashed it on the way out—petty to the end. But George Washington had it rebuilt and repurposed, and eventually, President John Adams renamed it Fort Independence in 1799. It was rebuilt again (because apparently the sixth or seventh version wasn’t enough) between 1834 and 1851 under Colonel Sylvanus Thayer, the same guy who helped shape West Point.

During the Civil War, Fort Independence was used more for training than fighting. It saw action again in World Wars I and II, serving as a coastal defense post. But mostly, it’s stood as a symbol—a big, imposing reminder that Boston knows how to defend itself. Today, it’s more picnic spot than military stronghold, and on sunny weekends, the place is packed with joggers, kite-flyers, and people chasing their kids around the lawn.

But step inside the granite walls and it’s quiet. Heavy. Historic. Volunteers sometimes give tours, walking you through vaulted chambers and long corridors that feel like they could still echo with cannon fire. Fort Independence isn’t a secret, but it feels like one. A relic hiding in plain sight, just a quick detour from Route 1 and a reminder that Boston’s defenses weren’t just about guns—they were about grit.