Prison Books (alternatively, Trap Books) are Linking Books to desolate Ages, and no other Linking Books to return. The D'ni used this method to punish and isolate unwanted persons. Canonically, the first instance of a prison book is in The Book of Ti'ana, which was used to trap Veovis (though he later escaped), though prison books appear several more times in the series (most notably Myst IV: Revelation and Riven). Atrus also created prison books and altered their Linking panel to show rich and flourishing worlds to lure greedy explorers (which trapped his two sons, Sirrus and Achenar). Sirrus and Achenar were 'prisoners' in Spire and Haven.
According to Atrus' plan, Gehn also was trapped in one, thinking that he would link to D'ni.
In Myst IVEdit
In Myst IV: Revelation, The Stranger revisits Atrus and is asked to use the linking books to Spire and Haven, which are implied to be the same prison books from Myst (Richard A. Watson seems to confirm this when asked about the two brother's fate, though fans specualte otherwise. See the Red Book/Blue Book pages for more information). The dates of the journals kept by the brothers indicate that they have been exploring their respective Ages for the last twenty years, which is precisely the amount of time between Riven and Revelation.
Fans who disagree with Richard A. Watson's revelation speculate that one of two things happened to release the brothers from their trapped position in the "void between Ages." Firstly, Atrus may have altered the Trap Books before destroying them in order to "free" the brothers by completing the links. Secondly,they speculate that the act of destroying each Trap Book forced the link to complete, dumping the brothers in their new homes. They also speculate that it might be necessary to both alter the linking book and then destroy it in order to accomplish this.