Traveling west on HW-26 and was a few miles outside Washtucna, WA. There is some rocky, rolling terrain that can block your view down the valley but as I turned a corner there was a large white craft that came Into view. It was maybe 1500' off the deck and traveling at a constant speed, approximately 200kts headed east and was 1-2 miles from the highway. The light color was brilliant white-blue that almost hurt to look at because it was late at night. It lit up the entire valley the highway parallels. I of course hit the brakes so could get a better look and in 30 seconds it was gone from view. It was intially very startling to see something that large and bright as I have plenty of experience flying small airplanes so I knew instantly this was not a blimp or something. I had no sense to grab my phone for a picture, but I doubt it would have been a good shot anyways plus I was driving a box van so I wanted to stay on the road. The craft was almost perfectly eppisoidal and looked greater than 400' long and maybe 75-100' tall. Definitely the biggest thing I have ever seen close up and probably a once in a lifetime sighting. The craft kind of reminded me of the larger ships Charles Hall describes in his books Millenial Hospitality, plus it was a warm summer night as I was driving thru some of that scab land. Fits the profile, but who knows. It was a overall shockingly awesome experience but I didn't notice any lost time or anything out of the ordinary after the sighting. Though I was very glad my dog was with me for company after that, ha.