Portland Japanese Garden in Washington Park is a jewel in downtown. Easily accessible by bus, it's a calm oasis and full of interesting features. I arrived at 1 pm just in time for the tour. The tour was very enjoyable and informative and the guide was lovely. If you don't know much about Japanese Gardens (I didn't!) I would suggest going when the tour is on as it will bring the garden more to life.
The Gorge + Mt. Hood