Marco,
There is a ferry. When we were still in Chicago area a bunch of the married couples from our church did the trip one weekend. Do a Google search on "lake michigan ferry". I did and came up with 2 different companies. As I remember, it was about a 4 hour trip across.
Any way you go, have fun.
Mike

Unfortunately, they both start in Wisconsin, so you need to factor in that driving time as well.