Being from MSP originally and having worked at that airport for a while, I have to also point out that the Mall of America is VERY close to the airport. You can take a train there and arrive in 10-15 minutes (not including time waiting for the train, should be every 10-15 minutes in the middle of the day). Less than a $3 ride, and your ticket lasts 2.5 hours (so if you get back to the airport that quickly, you don't need to buy a return ticket)