A couple great garden experiences are the Japanese Garden (6 acres and beautiful) and International Rose Test Garden (less varied but still well worth a visit). Waterfront Park along the Willamette River is a great place to walk or go bike-riding. If you like boating, the Portland Spirit River Cruise is an engaging way to spend a couple hours. If it's raining, the Art Museum (www.portlandartmuseum.org) is reasonably impressive.