I've gone to Hudson's now and then for about 65 years. They have the best hamburgers in the world. There is no fluffery. Pickle, onion, or cheese are all that they put on them. The meat is locally raised lean beef especially prepared for them. I'm not sure if it is salt they put on it; we always thought it was some kind of secret stuff. A lot of locals are in there, and half of the fun is the chatting about local stuff that goes on.
I went to high school with Roger Hudson, the father of Todd Hudson, who runs it now, and I ate there when Roger's father Howard ran it. A few years ago a McDonalds was put in half a block away. It lasted about a year. Hudson's would be packed and one person would be in McDonalds. Shows you how savvy the people are in Coeur d'Alene.
By the way, you can buy a container of the magic sauce. I don't remember how much it costs. I recall that when I was a youth we would watch in great anticipation when a tourist would load up his burger with the sauce thinking it was ketchup. It was quite sporting when the steam came out of his ears!