Red Rock Canyon is close to Las Vegas and sooooo worth the trip if you're in the area! There are hikes you can do, but make sure to go early to avoid the heat. The 13-mile drive inside the park is a one-way loop, making it easy to pause and enjoy the views/get great pictures. $7 park entrance fee.
It's not too crowded as far as parks go; the gift shop has tasteful schwag. There are picnic tables throughout the park so if you heed my advice and get a sandwich from 'wichcraft inside the MGM Grand hotel you can have lunch in the great outdoors!