I was gonna suggest Chuckanut when I first saw the subject line...
If you want some really amazing scenery, head a few hours south down I5 to Castle Rock, and turn off onto Highway 504 westbound (don't worry, it's not a divided freeway or anything). An hour or so on this very windy road headed up the mountains, and you'll end up here: Castle Rock, WA, USA to WA-504 E/Spirit Lake Hwy - Google Maps
If what you see there doesn't blow your mind, then your mind is unblowable.
As far as something closer to home, try a day trip out to Hope, up the Fraser Canyon to Lytton, take highway 12 to Lillooet, then highway 99 back down to Pemberton and then on home via Whistler and Squamish. This is a gorgeous trip through some incredible Coast Mountain scenery, and yes, some very twisty roads with a few very steep sections. It's 8-9 hours' total drive time, more if you're stopping to sight-see, so plan a full day, preferably before it gets too late in the year (so you have more daylight). Vancouver, BC to Vancouver, BC - Google Maps