From Seattle:

North Cascade Highway (Highway 20)
Take I-5 to Burlington/Anacortes. Go east on the North Cascade Highway (Highway 20) and follow to the town of Winthrop. Highway 20 is typically closed in mid-November. It re-opens in early Spring.

Steven’s Pass (Highway 2)
From Seattle, take 520 to Interstate 405 north to the Monroe cut off (it will say Wenatchee). Or, take Interstate 5 north to Everett and take Highway 2 east to Monroe. At Monroe, go east on Highway 2 to Wenatchee. Just prior to entering Wenatchee take the Highway 97 Exit, crossing the Columbia River at that point. After crossing the river, turn left at the first stoplight. Continue to follow Highway 97 to Pateros. At Pateros, turn left onto Highway 153 (turns into Highway 20 at Twisp) to Winthrop.

Snoqualmie Pass (I-90)
From Seattle, go east on I-90 1 mile past Cle Elum. Take the exit for Highway 970 to Wenatchee. Highway 970 will turn into Highway 97. Follow Highway 97 to Wenatchee. Just prior to entering Wenatchee take the Highway 97 Exit, crossing the Columbia River at that point. After crossing the river, turn left at the first stoplight. Continue to follow Highway 97 to Pateros. At Pateros, turn left onto Highway 153 (turns into Highway 20 at Twisp) to Winthrop.