Day trips from Portland. Obviously these work better as over-night trips, or more, but there are numerous ways to cut them shorter. Also, I list more activities along the way than are probably feasible.
1. Oregon Coast Drive. Follow Highway 30 from Portland to Astoria. Along the way, Scappoose Bay Marina at Warren offers kayak rentals and many miles of backwater channels to explore. In Astoria, numerous seafood spots and microbreweries along the boardwalk. At the east end of the boardwalk, Columbia River Maritime Museum is worth a visit, and even if they're closed the historic ships moored at their dock are worth a look. Half-day fishing charters, harbor tours and such can be booked from the marina. Continue south on Hwy 101. There are dozens of small towns, beaches, waysides, and trailheads along the way. (The entire coast is public land.) In Tillamook (eat the cheese, smell the cows...) divert to the Three-Capes Scenic Loop. (Part of this route is still blocked by a landslide, but the detour is marked.) Visit Cape Meares Lighthouse. Hike along Cape Lookout. (Tillamook Bay and the rivers feeding it offer white-water and flat-water kayaking, but you may need to BYOB.) Rejoin the 101 and continue south toward Newport. Visit Yaquina Head lighthouse. Do check out the tide pools and climb down the steps to the cobble beach. (If there aren't a lot of people around, record a couple minutes of the sound on your phone.) In Newport, cross the Yaquina Bay Bridge to South Beach and see the Oregon Coast Aquarium (and nearby Rogue brewery.) Head back across the bridge and down to the bayfront for numerous dining choices, and stroll past the fishing fleet along the commercial docks. Either cut across the coast range to Corvallis on Hwy 20 or backtrack to Lincoln City and cut across on Hwy 18. Take 99W to McMinnville. Stop at the Evergreen Air & Space Museum to see the Spruce Goose and maybe hit the 747 Water Slide, then drive through the Pinot Noir wine country back to Portland.
2. Columbia River Gorge and Mt. Hood.
Follow I84 out of town, but get off at Troutdale and follow Route 30 (Historic Columbia River Highway). (You can stop for a bite or a drink at McMenamins Edgefield estate, but then you might never get out of town.) There are numerous viewpoints, waterfalls, and trailheads along the way. Multnomah Falls is the biggest tourist trap in the state - this road will take you right to it, but there may be no place to park on a weekend. Before you get to Crown Point, watch for the Portland Women's Forum - duck into their parking lot to take pictures OF Crown Point - this is the angle you see on the post cards. Rejoin I84 at Dodson and continue east. Bonneville Dam has a visitors center and there are dozens of trailheads along the way. The Eagle Creek trail is very popular, but currently closed (unofficially - some people are scrambling around the missing bridge.) Several sections of the Historic Highway along here are reserved for bicycles and pedestrians only, e.g. from Dodson to Cascade Locks, vicinity of Starvation Creek, and most popular- between Hood River and Mosier.) One can book riverboat excursions at Cascade Locks. Continue to vicinity of Hood River. Numerous dining and microbrewery choices in downtown Hood River and on the waterfront. If wind sports are your thing, this is the place - kiteboarding, windsurfing, weird foiling boards. Or just watch the mayhem on the river. You can also rent SUPs, kayaks, bicycles etc. (I myself have an airbnb listing in this area that includes guest bicycles.) You can continue on to The Dalles, cross the river and follow Washington Hwy 14 to tour numerous wineries (getting into merlot/cabernet territory) and end up at Maryhill Museum - weird fine art museum in the middle of nowhere (long story), Stonehenge Replica, fruit stands, etc. Hike a bit of the dry side with trails at Horsethief lake that go past ancient petroglyphs carved in the rock, or up on Dalles Mountain (better during wildflower season in the spring.) Cross the river on Maryhill bridge and back through The Dalles. Take the scenic Hwy 30 route from TD or Rowena. This bit appears in every. damned. car. commercial. (They're filming yet another one today.) Catch the view at Rowena Crest (more trailheads) then back to I84 at Mosier. From Hood river, take Hwy 35 toward Mt. Hood through the apple and pear orchards of the Hood River Valley. Several possible mountain lakes to visit for hiking, kayaking, etc. Near Government Camp, visit Timberline Lodge for great views, summer skiing and day hikes. Head back to Portland on Hwy 26. (Maybe hit Edgefield on the way back through.)