From Boise Airport:
Head east on I-84 for around 40 miles to exit 95 for Mountain Home. Turn left on Highway 20 and continue for around 80 miles to the Highway 75 junction. Turn left on Highway 75 and continue for 25 miles to Main Street in Ketchum. Turn right (east) on Sun Valley Road and you'll reach the Sun Valley Resort in about a mile.
From Twin Falls Airport:
Take Airport Road east and turn right on E 3400 N then left on N 3000 E and continue through downtown Twin Falls. Continue straight on Highway 93 (Blue Lakes Blvd.). Continue on Highway 93 for around 24 miles which will turn into Highway 75 at Shoshone. Continue 54 miles to Ketchum. Turn right (east) on Sun Valley Road and you'll reach the Sun Valley Resort in about a mile.