We went to Winthrop with four of our friends a few weekends ago. It was amazing—great weather, big laughs, wonderful food and many many lawn games. We loved it so much we're planning to make it an annual trip.
If you go to Winthrop, drive there on the North Cascades Highway (it's breathtaking), bring a bike, try the cinnamon rolls, go to The Mazama Store, and drive up to Sun Mountain Lodge—the views are amazing. (Also keep an eye out for bears and rattle snakes.)