Piranesi

The turning point occurs when Piranesi finds a message written in chalk warning him that the Other is a liar. Eventually, a new person arrives, whom Piranesi calls "16." Through his interactions with 16, Piranesi learns the truth: the Other is a magician named Andrew Ketterley, who trapped Piranesi in this other dimension to steal his knowledge. Piranesi is actually Matthew Rose Sorensen, a modern journalist who went missing years prior.