The Japanese Garden is a must. It changes everytime I go there and works as a nice walk. Other than that, Portland is a very vibrant city and I much prefer it to Seattle. If you want to plan a day trip, then I'd head out to Mt. Hood and/or the Columbia River Gorge.
I haven't been to Portland all that often, despite my aunt and uncle living there. Though those are the things I often do when I head out there.
is a really nice airport with superb views of traffic from the top of the parking garage.
Enjoy your stay
The air in the clouds is very pure and fine, bracing and delicious because it's the same the angels breathe.