The Oregon Coast is not far from Portland. Head to Seaside for some traditional touristy fun on the boardwalk, or Cannon Beach for nicer shops and a slower pace.
Portland is equal distance from the coast and the mountains. The hikes on Mt. Hood in the summer are amazing.
Multnomah Falls is one of the tallest year-round waterfalls in the United States, and is the most visited natural recreation site in the Pacific Northwest. You can hike to the top of the falls, hike a little ways up or just enjoy the falls from the bottom (no exertion required). Either way, it's a quick 30 min drive from Portland, and you get to enjoy part of the Columbia River Gorge as a bonus. Hit the Troutdale outlet stores for some quick shopping on your way back to town.
With great views of the city, this is definitely a Portland bucket list location.