Whether you're traversing the William Powell Bridge on two feet or two wheels, any Miamian who exercises knows the difficulty of conquering the Rickenbacker Causeway. Beginning at the southern end of Brickell and connecting the mainland with Virginia Key and Key Biscayne, the five-and-a-half-mile stretch of the Rickenbacker is probably the most challenging running route in the county — but also the one that offers the most reward. The view from the top of the William Powell Bridge (AKA "the tallest hill in Miami") offers sweeping views of the downtown skyline and of the deep-blue waters of Biscayne Bay. You just have to get up there first.