I have driven the Columbia Gorge innumerable times and never get tired of it. It is always a place I take visitors, with its many waterfalls, scenic viewpoints, and beautiful hikes. If you have time while in Portland I highly recommend it.
The gorge was created from basaltic volcano flows and the Missoula floods. The book “Bretz’s Flood” by John Soennichsen is great way to learn about how those floods formed the gorge.
If you have a half day, Multnomah Falls is a must; one of the highest falls in the US. These are some high points, travelling from the west end to Multnomah Falls, starting in Troutdale and driving the Historic Columbia River Hwy. A first stop could be the Vista House at Crown Point, a wonderful viewpoint above the gorge. Continuing east, Latourell Falls has a 2.4 mile loop hike to the upper falls. Next is Bridal Veil Falls where a 0.3 mile trail takes you to the base of the falls. Wahkeena Falls has a variety of trails to take you to different views of the falls. And finally, it’s Multnomah Falls, which often has its highest flows in the spring, and is always beautiful.
If you have a full day, you could continue on to visit Hood River, with its brewpubs and fun shopping district. Then it’s on to Biggs, where you can take a bridge to the Washington side of the Gorge and visit the Maryhill Museum and a full-scale replica of Stonehenge.
More detailed information can be found at Gorge Friends.
If you can’t drive but want to see the Gorge, check out Columbia Gorge Tours.