Peaks Island is known for its picturesque oceanfront cottages, the iconic ferry dock often captured by Instagrammers, and the charming Inn that greets you as you walk up the hill. However, many people don't know that an abandoned World War II fort is located on the island with a mysterious underground tunnel open for exploring.

Battery Steele was placed on the National Register of Historic Places in 2005. Over the years, vandals (or artists) have claimed the walls as their canvas, creating elaborate painted works on the once bare walls. The fort once protected Casco Bay and much more, as it was the largest battery ever built in the United States.

According to the Oceanside Conservation Trust, two guns were mounted in the bunkers and an underground tunnel big enough for a truck to pass through connected the two bunkers. When the guns were fired "the whole island trembled."