Visiting the Alvord Desert Campground is a must in Eastern Oregon.  If you book a campsite, you have private access to drive out on the desert playa, and that also includes access to the hot springs.  Well worth it.  The stars out there are incredible.  Be sure to check the weather before heading out on the playa, because if it has been raining it will be incredibly muddy and very easy to get your car stuck in.