We stayed in a cabin inside Yellowstone for a long weekend, drove to SD and stayed in a cabin south of Mt. Rushmore for a week. Stopped at Martin's Cove on the drive back to Utah. Don't really remember the drive, it was well over a decade back. Any drive across Wyoming is torture for me. Western, especially northwest Wyoming, is awesome, stunning, beautiful... The rest of Wyoming is torture. Fill up with gas before driving across the middle of Wyoming. There are stretches where you go about 200 miles without the option for filling up with gas.

The Black Hills area is full of fun things for young and old. The entire area for 50 or so miles in many directions is like an amusement park or a collection of literally hundreds of small amusements and attractions. There are attractions of every variety. Zoos, caves, crazy houses, ghost towns, western reenactment/ recreation towns, museums, animal parks, mines (including the option to pan/ mine for gold, etc.), hikes, zip lines, alpine slides... You should be able to fill many days with things your group enjoys, unless you're interests are focused on big city fun. Custer is a cool town too, not far from Rushmore to the south. Devils Tower and Crazy Horse Memorial are awesome.

Unless you are a biker, consider avoiding going the last week of July through mid-August or so. The Sturgis rally completely dominates the entire area for 100 miles for the last few days of July through 10 days of August. Last week of July to mid-August or so there is a heavy influence from the Sturgis rally. If you are going anytime close to the Sturgis rally and want to avoid the craziness of Sturgis, stay south of Mt. Rushmore, like Custer or that area.