Going down most mountains is much harder on your legs than going up. Even if you only visit a rim, go down into the canyon a few hundred yards and then come back up. Most people do not attempt this. Park Rangers are stationed a mile or so down the path who advise ill-prepared hikers to turn around.
To avoid the crowds at the GC, get there late in the day and stay overnight. Early the next morning the rim is virtually empty. My wife, like some other people, suffered from altitude sickness. If you are over 62, get the National Parks Seniors Pass which lets you bypass the huge queue of cars waiting to get into the park.
https://www.nps.gov/planyourvisit/passes.htmThe best part of the walk is at the bottom where you sit by the river. If I might include this sentence from the blog.
Late in the day, we all wandered down to the bank of the river. Nirmal and I stayed longer than the others, watching the river flow by. He remarked that this was his favourite part of the trip so far, just watching this river. 'This river doesn't have to prove anything', he said.ray