I like both of Jim’s recommendations, but neither is in the Willamette Valley. I think you need to learn more about the Willamette Valley, because it may not be the place you want to be, particularly if you’re not interested in wine.
The Willamette Valley is primarily farmland. It is relatively flat, with a few rivers coming out of the Cascades (Clackamas, Molalla, Santiam, McKenzie) or the Coast Range (Tualatin, Yamhill, Luckiamute, Mary’s, Long Tom). There hasn’t been significant forest land on the Valley floor since before the Europeans came. The Native Americans used to burn the valley floor to make it easier to hunt there. The Missoula floods dumped about 50-75 feet of soil on the original valley floor, and the rivers cut through that soil, so rivers tend to have high embankments, leading to flat surrounding land. Finding a place where you can walk out your door and go hiking through a forest are, at best, few and far between. Now, the Valley floor is almost entirely dedicated to agriculture (berries, hazelnuts, nursery, hops, grass seed, wheat are all big).
When Portlanders (and whatever the rest of us the the Valley are called) recreate, they tend to travel to the Coast or Hood River, or over toward Bend. In the Valley itself, it would probably make more sense to find a nicer city to use as a base (McMinnville, Salem, Corvallis, Eugene come to mind), and plan activities in the surrounding area.
Oregon has a very good state park system, and there are a number of good ones in the Valley, including Champoeg (one of the first areas settled), Silver Falls (lots of cool waterfalls), Willamette Mission (more history), and Fort Yamhill (the only place the government built a fort to protect the Native Americans from the settlers).
