USS Constitution

The USS Constitution is the oldest commissioned warship still afloat in the world — launched in 1797, she fought in the Barbary Wars and the War of 1812, and earned the nickname 'Old Ironsides' when British cannonballs were seen bouncing off her oak hull during an engagement with HMS Guerriere in 1812. The ship is berthed at the Charlestown Navy Yard and is still a fully commissioned vessel of the US Navy, crewed by active-duty sailors who give free tours.

The ship is surprisingly large — 204 feet long, carrying 44 guns across three decks, with a crew of over 450 during her fighting years. Below decks, the cramped quarters where hundreds of men lived, slept, and fought give you an immediate appreciation for the physical reality of 19th-century naval warfare. The gun deck, where cannon teams worked in near-darkness during battle, is claustrophobic even as a tourist — imagining it during combat, with smoke, noise, and cannonballs smashing through the hull, is genuinely unsettling.

The Constitution turns around in the harbour once a year on July 4th, firing her cannons in a tradition that draws tens of thousands of spectators to the waterfront. The adjacent USS Constitution Museum (free, donation suggested) does an excellent job of telling the ship's story through interactive exhibits that let you try hauling on the rigging and loading a cannon. The ship and museum together are one of the best free attractions in Boston.