Great Falls or Bust

In just over a week, my wife and I are indulging our love of history, nature and rustic National Parks lodges with a trip to Yellowstone National Park. Our half-way stopping point is Great Falls, Montana, where we already have a room booked at the O'Haire Motor Inn and plans to have dinner and drinks at the Sip n' Dip. That much is a given (and my wife is holding out hope that they'll let her swim around in mermaid fins). But is there anything else in Great Falls that we should be aware of? Good vintage stores, liquor stores, alt-culture stores, etc.?

Thanks for any recommendations!