Needles Eye Tunnel, Custer State Park, South Dakota

The Needles Eye Tunnel, completed in 1922, is a narrow, one-lane passage carved through a granite spire in Custer State Park, South Dakota. As part of the Needles Highway (SD 87), this engineering feat measures only 8 feet 4 inches wide and 11 feet 3 inches high, necessitating careful navigation for vehicles. The tunnel is named for an adjacent rock formation shaped by erosion, and it remains a key feature of one of the Midwest's most striking mountain drives. The highway connects the park's spire formations with routes leading to Sylvan Lake and Mount Rushmore.