Fort Knox

Fort Knox is a granite fortification on the western bank of the Penobscot River in Prospect, Maine, that was never fully completed. The thick walls and long corridors connect casemates, gun positions and storage rooms across multiple levels.

Construction began in 1844 after tensions with Britain over the border between Maine and Canada. Work slowed after the 1860s as the threat from British naval forces declined, and the fort was never fully armed or garrisoned.

The name honors Henry Knox, first Secretary of War of the United States, who served during the American Revolution. Visitors today see the massive granite blocks and vaulted chambers that show how soldiers once lived and worked inside this coastal fortification.

The fort is open from May through October, and guided tours run between 11 AM and 3 PM. Admission also includes access to the nearby Penobscot Narrows Observatory, which is reached by a separate bridge.

The underground powder magazines were built to maintain a constant cool temperature for safely storing ammunition. These rooms are connected by narrow staircases and low passageways that visitors can explore today.