Ultimate Frisbee/Soccer/Softball - Bring some equipment and start up a game at one of the various fields and courts around the island.
The Anna Scripps Whitcomb Conservatory - Visit this historic greenhouse with numerous plants, flowers, and more in 3-4 separate climate rooms. Open Wednesdays through Sundays, 10am-5pm
Beach and Water Slide - Relax and splash around at the only open public waterfront in Detroit. $3/person also gets you a pass for the nearby water slide. Open daily, second week of June through August.
Belle Isle Nature Zoo - Visit this small nature center, detailing the life and animals of the island. See the small deer that have lived on Belle Isle for generations. 10am-5pm daily,
Free for the island, zoo, and beach; $3 for water slide
Belle Isle brochure - http://bit.ly/BELLEISLEBROCHURE