Portland is a Northwest city, similar to Seattle, which means you want to visit in the summer months.  It is a little more mellow than it's sister to the north, but still offers much in the way of entertainment, outdoor activities and general relaxation.

Not overwhelming, like many larger cities, Portland will allow your pulse to slow, while still keeping you entertained.   

There are the typical things to do in town:  boutique shopping, restaurants, and the stellar Powell's bookstore, and the various neighborhoods (which are conveniently divided into NW, NE, SW, SE quadrants); but the real "must-see" things you will need to drive to, as they aren't right downtown.  Multnomah Falls are spectacular, and there is a small hiking area close-by.  Slightly south of Portland is some great wine country.