It'd be easy to take a trip to Leavenworth/Wenatchee, visit the Rocky Reach Dam, Museum of the Columbia, the Pioner Village and the Aplets and Cotlets factory/store in Cashmere, go to LEavenworth and window shop, play at the Riverfront Park, and go on all kindds of beautiful hikes. I'd recommend staying at Sleeping Lady Resort in Leavenworth, but there's lots of camping and other hotels and places to stay.
We also love Winthrop/Twisp area. The Sun Mountain Lodge is lovely, but we also like the Chewuch Inn, which is walking distance to the village, and has cute simple little cabins and a wonderful breakfast every day. And the owners are super nice. There's all kinds of outdoorsy stuff to do in Winthrop- horse riding is big, and fly fishing and hiking.... there's a natural health/yoga yurt kind og retreat up there too, though I can't remember the name.
Coulee/Soap Lake makes a good trip, too. Camping is nice, there's lots of hiking and swimming and if the dam tours are going it's interesting. They do a laser show on the side of the dam at night, which is pretty fun.
Of course Yakima is nice, too!
We've got a nice museum, there's beautiful hikes, a huge, public observatory an hour away in Goldendale,
the Yakama Nation cultural center 30 minutes away in Toppenish, and the train museum, amazing wineries all over the place, and tons of festivals all summer long.
What kinds of things do you like to do?