Fort McKinley, Maine, Military heritage site on Great Diamond Island, Maine, United States.
Fort McKinley is a military fort on an island off Maine's coast, preserved with stone buildings, gun emplacements, and residential quarters from the 1800s. The entire complex spreads across wooded and open terrain with views of the water and surrounding islands.
The fort was built in the 1890s as part of America's coastal defense system and served for decades protecting Portland Harbor. After World War 2, it gradually lost military importance and was later abandoned.
The site is named after an American president and still shows traces of its past as a military outpost in coastal waters. Visitors can see how soldiers lived and worked in this remote position.
The fort is reachable only by ferry from Portland since it sits on an island with no bridge access. Visits are best planned during warmer months when tours and ferry service are available.
The fort was paired with a smaller military installation on a nearby island, which now functions as an environmental education center. This unexpected transformation shows how old military structures can serve new purposes.
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