[5][2][6] Among their physical and perceptual modifications, they have the ability to control the passage of time, to slow it down to make a hundred years feel like a few weeks, and speed it up to match clock-time.

While robots traverse the mountain's terraces, trying to establish what material the edifice is made of, some of the crew travel to the planet's surface to supervise the construction of a power plant.

Reviewing Purgatory Mount in Locus, Paul Di Filippo wrote that Roberts is "one of the field’s most delightfully surprising, adept, and formalistically variant authors", and "[a]ll these trademark traits of his fiction come to the fore" in this book.

[6] Di Filippo said that while for much of the book there appears to be no connection between the two "widely and wildly disjunct parts", in the end "all is crystal clear, with consequential powerful impacts by resonance".

[6] Di Filippo concluded that by writing about "a concrete and recognizable near-term scenario and bracketing it with more Olympian moments, Roberts achieves a kind of Stapledonian perspective which places humanity’s sufferings and dreams in a larger context that finally gives them some sense and heft.

"[6] In another review of the book in Locus, science fiction critic Gary K. Wolfe described Purgatory Mount as a "strange, bumpy [and] compelling hybrid novel" that raises questions about "ethics, responsibility, and ...

[2] He said the near-future United States timeline reads like a "Cory Doctorow hacker dystopia", and the book's three sections resemble the Divine Comedy's three parts, Inferno, Purgatorio and Paradiso.

[5] Lawie remarked that while the book's single line that connects the two timelines with "almost no cognisance of Otty’s world" may disappoint some, the author's afterword "delivers a reward for the reader who has climbed to the top of Purgatory Mount.