If you're looking for an easy yet amazing hike in Glacier National Park, I'd recommend a walk along McDonald Creek. It's flat, but the water is absolutely amazing. There's nothing like that turquoise water running through rocks that have been carved over the years. We did this walk after a much longer (and exhausting) hike and it was a great way to tend the day. We even took off our boots and stuck our feet in the water for a while. That glacier run off is cold!! This is one of those places where a lot of people just park their car and take a picture, but it's definitely worth a walk. You can get away from the crowds and see a whole lot you'd miss otherwise.
This road goes through the park and the creek runs along it for a while.