North Head Lighthouse
Lighthouses flash their lights at intervals that are unique to each one. NH lighthouse flashes at 6.5 and 21.5 second intervals. The lens is rotated by electricity, with generator backup. The existing light can be seen 17 miles out to sea. We weren't allowed out on the deck, as the rail has rusted through in two places, but there wasn't really a reason to go outside, as the inside view had more than your eyes could handle.