I can't lie, I was disappointed to be anywhere after the day at Yellowstone--anything was going to be a letdown. The fact that there is a whole lot of nothing in Idaho does not help.
We took I-20 to Craters of the Moon National Monument. The road went straight for awhile and then skirted a series of brown mountains. Eventually we got to Craters of the Moon National Monument. Spoiler alert: it was still empty!
This is where a series of volcanoes erupted/exploded all over the plains of the Snake River basin. The mountain-y bits are still technically there, but they're really small and unassuming. One would not guess that they barfed endless fields of lava for miles and miles.
Surprisingly (or not, really, since volcanic soil is quite rich), many trees and plants have sprung up. (Some died, like this, but plenty seem to be thriving.)
Seriously, endless miles of lava and nothing.
After a couple hours looking at various views of lava, we continued our journey westward. We passed into Oregon and had dinner, and then drove another hour to a motel in La Grande for our penultimate night.