We've been in Newhalem for a couple days at a North Cascades National Park campground. It rained all night, so today we went out looking for sunshine. When it's wet on the west side, it is often dry on the east side of the Cascades, so we headed east on Highway 20.
There are powerplant tours, Diablo Lake boat tours, and Newhalem walking tours (it used to be one big tour including Ross Dam powerhouse) but they don't start until July 3rd this year.
It's possible to do a wonderful loop trip using Highway 20 between Burlington & Winthrop, and then down to Chelan and Wenatchee before crossing the Cascades again via Highway 2 and Stevens Pass. Highly recommended!