Back in the days when many communities were isolated, librarians used to deliver books. The above linked article talks about those librarians who delivered by horseback during the depression. They were pretty amazing.
I loved looking at all of these photos in the article linked above. The only time I see a bookmobile these days is at the county fair. The kids are allowed to go in and look around. I usually arrive too late, so I haven’t gotten a really good look inside to see if they have books for older people. I also wonder how these children will return the books once the bookmobile leaves the county fair.