Take the Kingston exit from I-90 and go up the North Fork of the Coeur d'Alene River, through Pritchard, and go about 12 miles more, past Devil's Elbow Campground, and turn left at the sign for Fern and Shadow Falls. The falls are about another 7 miles. The road is rough so an appropriate vehicle is recommended. I've seen passenger cars in there, but I wouldn't take mine.
On Yellowdog Creek in North Idaho.