Years ago I ran across a "secret" national park service cabin in the Apostle Islands. I had heard about them and it took a while to put 2 and 2 together. When I first questioned a ranger, she feigned ignorance. Only after I described the place to her did she acknowledge it. I've told people about it in the first person. I would never post it on a forum like this. I don't know if they still exist. I think the original intent was shelter for a ranger caught out in bad weather.