Modern Marvels: Until recently, the Mackinac Bridge was the longest suspension bridge in the world. One of the top engineering marvels of the 20th century, the bridge spans the 4-mile wide straits of Mackinac, where Lakes Huron and Michigan come together. The Mighty Mac connects the pastoral northern mainland of Michigan with the state's heavily forested Upper Peninsula and stands as a testament to the dreams, determination, and hard work of a small few who created a true masterpiece of modern engineering.