The Chilly Hilly is one of the great bike classics of the Puget Sound Area. As the name implies, it takes place in late February every year, heralding that the worst of winter has passed (Chilly) and that the route is full of rolling hills, with one or two major climbs thrown in for good measure.
While the organized ride is worth it for being part of a bicycle takeover of the Washington State Ferries alone, I actually much prefer the non-organized version of the ride. The route is mostly through quiet, forested backroads with the exception of crossing Highway 305, and has some great views across the sound.