Take I-90 to Cle Elum, then follow 97 north to Highway 2. That will take you into the town of Leavenworth. Drive to the end of town, and take a left onto Icicle Road.
This is Icicle Creek, near Leavenworth, Wa If you drive to the end of town, then turn left onto Icicle Road. There is a main parking lot, that you can get a good view of the creek, or you can take the trail for some better views. Although its pretty throughout the year, fall is the best time to go.