Entrepreneurship's Greatest Challenge: Rebuild Detroit

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Madison Building

Dan Gilbert's $12 million building renovation. The location was once home to a glorious theater that was razed for a parking lot. The building reopened last year.

Square feet: 50,000

Number of Ventures: More than 30

Welcome Back: One venture in the space is Chalkfly, co-founded by two brothers who ditched gigs in D.C. and Chicago to return home to Detroit. "The entrepreneurial renaissance over here brought us back," says co-founder Andrew Landau, 27.