The food. Great food all over the area. I have yet to find pizza or ribs that taste like they do in Detroit anywhere else.
There are several gorgeous, Catholic churches there that are over 100 years old. Old St. Mary's is 175 years old and it is still open and absolutely beautiful. There is also a fantastic, authentic Italian restaurant in Detroit called Giovanni's. Yum!
for some reason, the garage sales are pretty good there. One time I bought a CSN record that had a joints worth of weed in the gate fold.