Bonneville Dam is within a few miles and offers one of the best accessible tours of a dam. Tour the generators, the fish ladder, the fish viewing windows, and the fish hatchery. Skip Portland and continue west to the mouth of the Columbia. On the Oregon side is Fort Stevens State Park. In season, reservations are necessary at this park which features both river and ocean sites.
Restrooms are accessible and although there are no accessible sights, many work well.
For history enthusiasts, the Columbia is full of Lewis and Clark and early day discovery. Take about a month in the area to discover the flavor. August and September are ideal months to visit. The Handicapped Travel Club and H.T.C. News.