The Grand Canyon has to be one of the most amazing sights you could ever see. Since I'm not a big hiker, we opted to take the hop-on-hop-off Hermit Road shuttle around the South Rim of the canyon. It's free!
We mostly "hiked" between stops -- the trails were so easy my Grandma could do it; and we road the shuttle back to the beginning once we reached the last vista point.
The trails loop around the top of the canyon for some breathtaking views. Don't look down, you're on the edge!
You should allow a good part of a full day to do this unless you just want to be a lazy bones and ride most of the way. And there are several shuttle routes to choose from.