Probably too late.
But they Hoyt Arboretum is awesome for hikes and nature walks. All free too, you just gotta make sure you get there early. I recommend the Red woods deck and the 3 hikes around it. Its a beautiful path, generally pretty quiet with lots of things to see. Plus the redwood deck is pretty awesome.
I really like the Multnomah falls, but its crazy busy with people. I would suggest going to the neighbor falls. It has a nice hike up the mountain and by the side you see the river go down. Its a really nice one. There is also Crown Point vista, which has a beautiful view of the river and of Portland.
I have yet to go to Ground Kontrol. But the idea of a room full of pinballs sounds like a great time.
Oregon Coast stops. Cannon beach is awesome and as a Goonies fan you have to stop there and also Astoria. Really nice spots, but tbh, anywhere along the coast on a beautiful sunny day will be nice. You can see all the awesome rock formations and a windy road along the coast.
hmmm... like i said.. probably too late, but i was out and about most of the weekend and didn't get to post here until now.
Hope you guys had a good one tho.