The Grand Hotel opened on Mackinac Island in the summer of 1887. At 660 feet, Grand Hotel’s Front Porch is the world’s largest. They note that early on the porch became the principal meeting place for all of Mackinac Island, a promenade for the elderly, and a “Flirtation Walk” for island romantics. Their History photo gallery has a couple of cool photos of the porch from back in the day.
More about the Grand Hotel on Michigan in Pictures, and here’s a video look at the porch: