A few suggestions in that part of Oregon:
* Close to Bend, you can visit the Pine Mountain Observatory, which is open to the public in the summer. https://pmo.uoregon.edu/visiting/ - at 6000 feet, and far from anything, the views of the night sky even without telescopes are amazing. And the staff there point the scopes at interesting sights and explain what they are.
* Further out, Steens mountain and that area is incredible. It's one of the most remote parts of the US outside of Alaska.
* The Christmas Valley area has a lot of interesting things like Fort Rock, Crack-in-the-Ground, Hole-in-the-Ground and the sand dunes.