Thomcat
10/22/2025
More about survival / community building than the actual "tunnel", this is a solid Heinlein juvenile with strong female characters and ethnicity mostly unspecified - both ahead of their time.
This 9th book in the loose series was published in 1955, coincidentally just a year after Lord of the Flies. Students are again the survival group, but in this case both male and female. They also expect to be retrieved - this is a few weeks of survival course, at least at first. I would guess that some of the techniques came from Heinlein's Navy background, and were well written.
This later juvenile is also bogged down a bit by Heinlein's discussion of government. I'm sure the Malthusian overpopulation of Earth (leading to the colonization project framing the story) is also one of his standard talking points. Some of this slowed the story in segments.
Read this shortly before joining goodreads, didn't review it then - now corrected. Somewhere between 3½ and 4 stars.