If you're staying the night, The Inn On Ferry Street offers a great cozy experience and is in the midst of a lot of cool things Detroit has to offer in Walking distance -- http://innonferrystreetdetroit.com/default.asp?source=google+inn+on+ferry&gclid=CISj0oGcgKYCFY4J2godBB1Dlg. I own a cono in the building next door -- The Park Shelton, which is also home to a great Creperie (http://www.goodgirlsgotopariscrepes.com/) run by a friend of ours in the city. If you order "The Dana" -- it's named for my wife (and was designed by me).
As for things to do and see in the city, the Detroit Institute of Art is a fan favorite, and right near the Inn on Ferry and the Creperie. It's the third largest art institute in America and beautifully redone in the last several years, but if Art isn't your thing or your pressed for time, I'd aim for downtown and drive (or walk if its not too cold) around Campus Martius park (dead center in the city near Hard Rock Cafe), the stadiums, etc., Find the Gaurdian Building Lobby (500 Griswold Ave. Detroit, MI 48226) and take a peek at Real Detroit, a great shop with funky tee-shirts and other items inspired by the city. It's a small city downtown and traffic isn't difficult, so drive at your leaisure -- the architecture is really cool.
As for lunch or a great place for a beer, I urge you to go to The Detroit Beer Co. If you're an IPA man, get one or try the Porter, Detroit Red, or any of the hand crafted beers on tap. The food is generous and delicious -- it's where you'd find me on any given day in the city. If you manage a late night craving, or want the raw skinny on Detroit's best eats, try Lafayette Coney but not American Coney. Order the Chili Cheese Fries and prepare to be blown away.
You'll also want to stop in the GM Rennaisaince building, probably the most well know landmark in the city. It's built like a maze, but GM has lots of car displays and the river views to Canada are sweet too.
If you want to know more or have a broader view, just take your car from downtown after your visit and drive East on Jefferson Ave. The infrastructure and the drive tells a significant story -- from Detroit's toughest issues--population decline, blight, inner city poverty to beautiful pockets of homes and views of the water, etc...then, all of a sudden, the world changes and you'll be in Grosse Point -- pristine streets, middle and upper middle class, stunning homes, etc. This divide is as much racial as economic. So, it's really up to you how you want to navigate your time in the city.
If you're looking for more, at all -- there is no better resources for interesting and fun things than Inside Detroit: http://www.insidedetroit.org/. I worked with the founder Jeannette Pierce for a couple years -- she would definitely remember me and Dana. She's a fountain of knowledge and a storm of energy. She aslo has a storefront on Woodward ave downtown leading into Campus Martius.
I'd say, It's a complex city which has undergone a combination of devastating neglect and really amazing physical decline in some places ... it changes from block to clock. So, I understand it is easy to see that and wonder why anyone would want to live there or to look down on it, but there are real gems to discover and you'll find the people generally some of the nicest in the world. .