Although this book was far from perfect (or even great), it was weird, unpredictable, and engaging enough to let me overlook many of its faults.
The biggest fault, for me, was the seemingly forced addition of sexuality and sex scenes. Literally sometimes it was just a quick sentence to sort of remind readers that these are humans that want to have sex. The protagonists were teens, so it fits, but it didn't flow naturally in the story at all. Other than that, the writing just got a bit off and clunky sometimes.
The good was that I was consistently surprised by this old sci-fi book. I feel like I'm rarely surprised these days. But this story's setting was unique, as was the premise, giving it a fresh (to me) feel. The humans in the book are in a massive moving city of 25 million plus people. The city crawls across the land by disassembling the back and reassembling it at the front, for thousands of years. It turns out humans ruined the earth and some that couldn't get themselves to escape to space did this instead. In the city, it's very segmented, so if they go far in any direction, it's like a new country.
The characters are a bit bland and static, but it's two teen boys that are best friends and the main character's crush. They decide to stick together when an earthquake scares everyone else to abandon their area of the city and go on the Pilgrimage to the front of the city. What follows is a wild trip for the three. Somehow there's a semi-magical slave-driver that has taken over a whole segment of the city just to endlessly whip humans into dragging his cart around, looking for more slaves. They later meet giants, who turn out to be normal sized. So our protagonists are small in stature compared to us. Even later, they encounter humans that are so enmeshed with some hyper-advanced technology that they are immortal and have some level of super powers. These people draw them in and have sex with them and try to get them to join them. They escape though, only to later be caught by people even smaller than them in the city's jails. Others let them out, explain to them more about the history of the city, and then bring them to the front of the city, which has also been destroyed, to show them all the inhabitants feeling trapped outside the city, just sort of standing around the ocean beach - millions of them. And the slave driver is there with thousands of people pulling his now massive cart. The hero kills him, sort of, then they eventually decide to go live with some people that had been living outside of the city for a long time. However, most people went back to the ruined city to try to live (but likely die) there. A big realization was that they had been bred for captivity, whether intentionally or not is unknown because of how much history was lost.
Not sure of an overall message here. Perhaps it was anti-city in some ways, suggesting it breeds out characteristics of independence and self-sufficiency. This seems to then be equated with being slaves, preferring horrible lives as long as they're simple and easily understood lives. There may also be a small undercurrent of environmentalism, since it was hinted that humans destroyed the earth that way (as opposed to nuclear war which was so popular a worry back then).