I will drive an Enterprise Rent-a-Car one way from Roseburg, Oregon to Missoula, Montana. Most of the route is on Interstate highways.

On June 11 I drive from Roseburg to Ritzville, Washington. South of Ritzville I plan to detour to Palouse Falls to see it in late afternoon sun. The waterfall detour adds an hour of driving compared to staying on US 395.

On June 12 I drive to west Missoula and return the rental car after lunch. In the afternoon I will explore the Clark Fork river, downtown Missoula, and the University of Montana by bicycle. The second half of the day is car-free, so I'll call it day 1 of the bike tour.

The Return Trip

To get home I will drive an Enterprise Rent-a-Car one way from Twin Falls, Idaho to Roseburg, Oregon. 

Driving time is 1.5 days but I plan to make 3 tourist stops near Twin Falls to make it a 2-day return trip. 

1. Near Buhl, Idaho, a soak at Miracle Hot Springs, a commercial soak that I have never visited.

2. A two mile canyon/waterfall hike at Box Canyon Spring southwest of Wendell, Idaho.

3. A short hike on the rim at Malad Gorge northwest of Tuttle, Idaho.

Combined with the Snake river canyon rim trail, the two canyon stops will give me a good sample of the many basalt canyons in southern Idaho.
You have to go miles off dreary I-84 to see the scenic canyons.

After the tourist stops I plan to drive across Oregon on US 20 via Burns and Bend, crossing the Cascade Range at Santiam Pass. The two lane highways will be a nice change of scenery after driving the I-84 route six times in the last two years.

Altogether this will be a 22 day trip:
1.5 day drive + 18.5 day bike tour + 2 day drive