Helena! I'm in Portland but just had surgery on my hip and am pretty confined to a bed/sofa loop for a few more weeks now so I'm no good at showing you round our fine city :( But fine city it is! Fall is gorgeous, the leaves are already starting to turn and if you have a spare day to head out to the gorge for a day hike it coudn't be more beautiful. And yes, Mt Tabor is a volcano (dormant) within city limits, has multiple parks and a darned lovely view from the top. Trimet is the local public transit system and has super useful apps. You can even buy day (or week, or weekend) passes online without having to worry about exact change. What part of town will you be in? Powells and Voodoo are staples of the tourist trade. Willamette Week is a great (local) resource for events. Feel free to msg me at 703 798 5453 if you get lost or need a last minute idea. I can't really go anywhere but that means i'm pretty much always on call as a resource :)
eta: if you're near the convention center and ever just have an extra hour, go for a walk along the waterfront. The Willamette river bisects the city and is basically a huge park along both side of the river. You can walk up the east or west side esplenade north to the steele bridge and south the hawthorne bridge, both have pedestrian pathways and make a nice long loop with Japanese memorial at the NW corner and OMSI at the SE corner. Random sculptures and public art along the way.