"The Lavalite World" by Philip Jose Farmer (1977)
"Orc removed a little black book from a pocket, opened it, consulted a page, said something that sounded like gibberish, and the door opened. He replaced the book and stood to one side as the cage rolled into a large room. It stopped in the exact center."
The Lavalite World is, for all intents and purposes, the last book in Farmer's World of Tiers series. By some accounts, there are two other books in this series: Red Orc's Rage and More Than Fire. But Red Orc's Rage is only tangentially connected to The World of Tiers, and More Than Fire was written so long after The Lavalite World that one could easily regard it as apocryphal.
The Lavalite World, although written a whopping 7 years after Behind the Walls of Terra, picks up where the previous book left off. Kickaha and Anana are still on the Lavalite World, and still trying to foil the schemes of Red Orc and Urthona.
The writing in this novel is much more mature than that seen in previous installments, though there are misspellings, and some embarrassing grammar ("much potentialities"). Pacing is no longer an issue, the author does a better job of foreshadowing, and the characters' motivations are clear throughout. The ending of this book, which is (for all intents and purposes) the end of the series, also seems much less arbitrary. Farmer put a lot more thought into The Lavalite World, and it shows.
And I've got to say, you don't get more 70s than a science fiction novel about five people trapped inside a virtual lava lamp. There's even a black character who says things that white people think black people ought to say, and an escape sequence near the end that's delightfully weird. In many ways it's a throwback to the only other good book in the series, The Gates of Creation, but it's also its own creature, playing by a newer and more interesting set of rules.
The Lavalite World isn't high art by any stretch of the imagination, but it's a solid book that deserves to be read. No, it's not The Godmakers. No, it's not The Eden Cycle. No, it's not V.A.L.I.S. But as adventure stories go, it's one of the better efforts by one of the less famous science fiction writers. And while I can't recommend The World of Tiers as a series, I can recommend this book without any reservations.