Baltimore County, US
Fort Carroll is a 3.4-acre (1.4 ha) artificial island and abandoned hexagonal sea fort in the middle of the Patapsco River, just south of Baltimore, Maryland. It is named for Charles Carroll of Carrollton (1737–1832), a signer of the Declaration of Independence.
Listen to the audio guide for Fort Carroll Free on WIP — starts by itself when you arrive, even with the screen off