Of all of the parks I have been to, Yosemite National Park in California has to be the most serene. I think I can speak for the three of us when I say that our only regret was not planning more time around our trip here.
As it is, we pulled into the park sometime midday and unfortunately could only stay for about 3 or 4 hours. We took a few hikes down through some of the forests and also waded around in the lake in the middle of the park.
After a nice picnic in the park and plenty of photos, we had to continue northeast through California.