Willamette Falls has the best views for a truly unique display of natures creativity. There are plenty of rocks and grassy spots by the waterways you could chill out and smoke there. I would consider another park though if you want something very relaxing. Namely, Clackamette Park. The water is still there and it’s more of a place to bring a blanket and hang out for a while and do your thing. Check out the farmers market if you’re back in town and want to do some shopping. A lot of it is open air environment and you can smoke around there with respect to the people around you. There’s all kind’s of goods and stands with locally produced products.