I'm guessing Comerica Park. A couple Warped Tours were there. Or how about Hart Plaza where the Detroit Electronic Music Fest and the Downtown Hoedown are?
Incidentally, I just landed back home in the dirty D for the holidays.
5/8 - Master / Solstice ?
5/18 - PHF / Shit Life / Girth
5/19 - Primitive Man / GutRot ?
6/17 - SOAD / Melvins