Central circle with 12 large interlocking rings around it similar to a 'spirograph' pattern. Approx 300' in diameter.   

Central circle with 12 large interlocking rings around it similar to a 'spirograph' pattern. Approx 300' in diameter.   (photo 2)

Central circle with 12 large interlocking rings around it similar to a 'spirograph' pattern. Approx 300' in diameter.   (photo 3)