Go see some live jazz. There is jazz Tue-Sat in the lobby of the Benson. Goto
Jimmy Mak's on a Tue/Wed/Thur for a guaranteed good time.
Drink lots of beer on tap. Portland has some of the best beer in the world, and its varied and plentiful.
I'm not sure that it's much of a sight-seeing town. You could go hiking in the
Columbia Gorge , its pretty nice out there.
Others will have better ideas, i'm pretty much a homebody. However i will take you up on beers and lap dances if any of the above ideas prove to be fun.