I had an idea. There's a lot of hikes near Multnomah falls are good for a work out. I mean, I've only done two of them, Multnomah Falls and Angel's Rest, but I got a good work out. I'm not exactly athletic, though. I have zip on stamina.
Nevertheless, Angel's Rest is a really nice hike, and there's another beyond it that's twice as long as that (something falls, I forgot). You don't have to pay to hike any of the trails, either, but it's past Troutdale. It's a thought. Especially to go in a group.