After travelling the world promoting the book, Clark was struck down with acute Lyme disease, explaining why it's taken 16 years for another novel to appear.

Piranesi is a completely different novel, but equally original.

Clarke has documented her fascination with the 18th-century Italian artist Giovanni Battista Piranesi and his etchings of Roman ruins and huge prisons, images which flow over into her novel.

Clarke's main character, Piranesi, who says "as far as I remember it is not my name", lives inside the labyrinthine House, "an infinite series of classical buildings knitted together", with an ocean full of marine life occupying the lower floors.

As the narrative evolves it becomes clear that Piranesi has gone through a traumatic experience and sees the House as a refuge from a past that he doesn't wish to remember.

Clarke notes that while Piranesi is "in a very strange and in some ways inhospitable place, he doesn't feel it's inhospitable".

The reader follows Piranesi through his journal which begins in 2011.

Piranesi wonders, "Who is it that I am writing for?

"Are You a traveller who has cheated Tides and crossed Broken Floors and Derelict Stairs to reach these Halls?

"Or are You perhaps someone who inhabits my own Halls long after I am dead?"

Piranesi notes, "Since the World began it is certain that there have existed fifteen people". Thirteen of these are skeletons in the House, which have a particular significance for Piranesi, who is occupant 14.

Fifteen is an occasional mysterious visitor, the smartly dressed, "The Other", who seeks the House's "Great and Secret Knowledge" through Piranesi's explorations.

"The Other", who hides his access to the outside world from Piranesi, is concerned that another visitor, the "patient, resolute and ingenious", 16, will unearth the truth of Piranesi's former life, which Clarke slowly reveals towards the end of the novel.

When her illness was at its worst, Clarke mentally returned to a childhood favourite book, CS Lewis' The Magician's Nephew, in which she escaped to the alternate city of Charn, revelling in being "alone in a place like that, endless buildings but silent" .

Written before COVID-19, Piranesi's strange isolation, she has noted, is now reflected in many people's situation around the world.

Piranesi is a stunning achievement, visually atmospheric and philosophically haunting.