The “sailing around the world” experience was what immediately came to mind for me too. But it seems the families that do this type of thing are super-close and the parents are much more important to the kids than any other friends. Not always the most healthy situations for their later college experiences.
I would also think about planning a family gap year after high school graduation and doing that well in advance. That would give the kids something to look forward to instead of four more stressful years in college. I worked for a year before college and it was really helpful as a way to grow up and meet a very different set of people.