I live in Portland, and I am a member of the Chinese Garden. I can take you there as a guest. It closes at 5 PM. It is located at NW 3rd and NW Everett. All of the buses in Portland are free in the central part of the city, which is called fareless square.

I am not sure what else to say. Except bring your rain gear! Winters are mainly overcast, and drizzly.
Here is a link to the garden. If you are interested in other public gardens, I can take you to visit some.

http://www.portlandchinesegarden.org/

I strongly recommend that if you have a day to play around, that you visit the Columbia River Gorge. There are many waterfalls in the gorge.

Powell's books is interesting. It seems as if the store has gradually swallowed up all of the adjoining office buildings, which are now connected, with odd level changes between the rooms. I beleive that is is open until 11PM on every night.

http://www.powells.com/info/citytour.html

Have fun,
Mary