Ok. My main interests are history and geology, so keep that in mind.
I would strongly recommend a stop at the Applegate Trail Interpretive Center. It’s a museum off I-5 at exit 71. When I was there years ago, a crazy Vietnam vet ran the place, and just engaging in a conversation with him was worth the stop. However, by the looks of the website he no longer runs it. Anyway, it’s a fascinating look at the local history, and how southern Oregon and northern California were settled.
I would also recommend a day trip un the North Umpqua river. If you’re looking for a good place to stay for the night, the Steamboat Inn cannot be beat. Make sure to have dinner there, as it is one of the best retaraunts in the county. They have a cookbook published called “Thyme and the river”, which is my go-to cookbook when I’m entertaining during the holidays. seriously good eats.
The Steamboat Inn is also where novelist Zane Grey would hang out to detox from life.
If you go further up the river, check out Watson Falls. The entire area around Crater Lake is essentially a big plateau created from the Mt. Mazama eruption, and Watson Falls is literally at the edge of this plateau. No picture will do it justice, it needs to be seen in person. However, in late summer the falls may be just a trickle, so keep that in mind. In the same area is Grotto Falls, which is absolutely spectacular. A large waterfall with a natural cave behind it. The trail to the falls simply curves through the cave, taking you behind the waterfall. It is well worth the drive.
The entire western Cascades is full of fascinating waterfalls and short hikes. This area is where the volcanic activity that created the Cascades meet the coastal valleys, and the geography is absolutely stunning.
Crater Lake is spectacular, and worth the drive. I don’t know when your trip is, but try to visit before they shut down the rim drive for the winter. Give yourself several hours to tour the lake.
Much of this stuff is ignored by tourists, so they have few visitors. Crater Lake is popular, but mostly on the weekends. There is a lodge perched on the rim, which is another good place to stay the night. The mosquitoes are quite bad, I wouldn’t recommend camping unless you set up early in the afternoon.
Farther north, take a detour east to McMinnville and spend some time at the Evergreen Aviation Museum. The Spruce Goose is on display there, as well as a Titan II missile, a Blackbird, and a B-17 that you can enter and walk (well, crouch) through. It’s so far the only museum in Oregon that I have made a deliberate effort to visit more than once.