Martha,
I grew up in Portland, long ago. It has changed much. Have not been back for a couple of years, so some of this may be out of date.
I second the recommendation for Powell's Books. They have at least two locations.
Downtown Portland has several outdoor public areas with fountains.
Downtown Portland also has several indoor merry-go-rounds that have been restored by enthusiasts.
We used to go to Louis' Oyster Bar, origin of the salad Crab Louis, now in a seedy part of downtown. They used to grow their own crawfish in a lake in the Cascades. Have not been back for years. Worth asking about.
A couple of years ago, there was a private trolley car that ran from the industrial district just south of downtown to Lake Oswego and back on the hillside above the Willamette [pronounced will-AAH-met, NOT will-a-MET-ee] River. The snobs in Lake Oswego didn't like it very much because it ran through their back yards on an old interurban line, but the easement was still there although disused for a long time. A fun little trip, if it is still active. Call the tourist people before you leave for your trip as reservations may be required. It was very popular when we went on it.
Suggest you get a map at your hotel and ask the front desk about these things. Then call the tourist bureau for more info if you need it.
Portland is a pretty city at night. Consider having dinner or drinks at one of the restaurants on the top floors of buildings downtown. Ask at the hotel. Get a seat by the window and watch the river at night.
Oh, yeah. Portland does not have warm rain.
Bring a sweater and a raincoat. Buy an umbrella when you get there if you need it. Natives are issued one at birth.
The Portland Art Museum is a little south of downtown in the Park Blocks and may be worth your visit. They had a big collection of Northwest indian art plus the usual touring shows.
Enjoy!
Ed