We live about 10-15 minutes away from downtown Frankfurt, however, we haven't really explored much. We went to the mall last fall to get our Chipotle fix and now have ducked into the old town area. As far as where to go in the downtown area though, I'm still clueless.
It was super windy that day, so we had to cut our trip short, but we did make it to the Kleinmarkthalle - an indoor market that operates daily (I believe). It was cool to see and definitely worth checking out. It was an easy walk from the old town square above and had a bustling wine bar on the second floor balcony with tons of local wines for sale.