With all due respect, the Mall of America is just a mall. Okay, so it's a big mall and interesting by virtue of having a small amusement park in the center, but essentially it's a mall like many others.

I would second DavidDTW's suggestions. Even if you're not interested in the Walker itself, the sculpture garden is a nice place to visit. And the lakes... personally, to me the lakes and the houses in the neighborhoods surrounding them epitomize so much of the character of Minneapolis and I've enjoyed countless hours walking around them.