Hey, NowOrNever,
Here are a few links and things to help figure out where to go, what to see & do, etc. in and around Detroit.
First, you said you were interested in history and architecture. Try
www.preservationwayne.org. They're the leading local preservation org with lots of resources on historic architecture, rehab and redevelopment, etc. They offer regular tour programs from May to Oct, the biggest being the Historic Theater tour in August. I'm one of their guides. You can find similar info at
www.cityscapedetroit.org, whose mission is more general built environment-related than historic-focused.
A couple friends also started
www.insidedetroit.org, with their own tour program that includes restaurant/bar tour events downtown. Check out
www.experiencedetroit.com for more info on attractions and self-guided tours of all kinds.
For what's happening currently, our biggest local weeklies are the Metro Times (
www.metrotimes.com) and Real Detroit (
www.realdetroitweekly.com). If you're gay, check out
www.pridesource.com and the Between the Lines weekly for events, etc.
There's not much major shopping in the city. The chains are all in the suburbs. But amazing restaurants and goodies abound if you know where to look. For starters, check out Eastern Market (
www.detroiteasternmarket.com) and Pure Detroit (
www.puredetroit.com) for really unique stuff, much of it locally oriented.
There's lots of info on local development, new businesses and things to see at
www.modeldmedia.com. Several new orgs have popped up in recent years to breathe life into the city and civic realm in general with events, lectures, forums, etc. including
www.detroitsynergy.org and
www.createdetroit.com. They may have things going on while you're here.
For my money, the best events in town include the Memorial Day weekend Electronic Music Festival (
www.demf.com), Festival of Arts in June (
www.detroitfestival.com) and Dally in the Alley (
www.dallyinthealley.com) in Sep.
Someone mentioned the Henry Ford Museum & Greenfield Village in Dearborn. They're both at
www.thehenryford.org. They run tours of the Ford Rouge Plant, which is a pretty amazing, huge and historic factory complex. It's near where I work, and so is the Arab American National Museum, a one-of-a-kind place with surprisingly multicultural events and concerts programmed regularly (
www.arabamericanmuseum.org).
Dearborn is one of the few local suburbs worth hanging out in, along with Hamtramck and Ferndale. Ann Arbor is a half-hour drive away, or a little longer by Amtrak. Otherwise, there are tons of cool, off the wall things to do and places to go in Detroit neighborhoods like Southwest/Mexicantown, Corktown, Midtown, Eastern Market and Downtown. Surf around for info on Indian Village, Boston Edison, Palmer Woods and Brush Park and you'll see how Detroit's robber barons once lived, and how many still do.
You can probably search any of those places from the links above and find stuff to do. If those don't provide enough info, maybe you're being too ambitious for one trip. :-) Hope this stuff helps and I'd be glad to provide more if you need it.