Do Custer State Park as many times as you can. Go early morning or later evenings for the best wildlife viewing. We saw Elk, bison, deer,Pronghorn, big horn sheep, Turkeys, and more. Take plenty of crackers to feed the Begging Borrows, a huge hit for the kids!
Cosmos is strange and made us feel odd the rest of the day. Do bear country USA early or late in the day otherwise the animals will all be bedded up mid day. Do reptile gardens early in the week because your ticket is good all week, or at least it was 4 or 5 years ago. You can see Mr. Rushmore from the road if you don't want to pay to get in. Crazy Horse was only worth it because when we were there you also got into a rodeo on the grounds for free. The rodeo was low end but tons of morbid excitement as at least 4 or 5 riders were taken by ambulance. Needles highway is cool and be ready for photo opps when you can see Mt. Rushmore through some of the tunnels. We stayed in a cabin in Custer. A bit of a drive from some destinations but right by Custer State Park which allowed us to drive through when we wanted. Have fun!