Aerial view of Belle Isle Park in Detroit, Michigan; Shutterstock ID 1540818512; your: Bridget Brown; gl: 65050; netsuite: Online Editorial; full: POI Image Update

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Pretty Belle Isle floats in the Detroit River. The entire expanse is parkland where kayaking, walking trails and a glass-domed conservatory await. There's a beach, zoo, aquarium and maritime museum, too. Once you pay the entry fee, the individual sights are free. The cycling here is terrific.