Labyrinths of the Mind was a 24th century manuscript written by Betazoid Doctor Marina Derex. It was published in 2371, at which time only a few thousand copies were produced. Derex hid her piece of the map to the Progenitors' technology with the original handwritten manuscript in the Eternal Gallery and Archive. Near the back of the book was a large metal card with Betazoid text on the top, depicting a maze with a large symbol in the center. When touched, the person would be transported into a mindscape to be tested for their worthiness to find the Progenitors' technology. (DIS: "Erigah", "Labyrinths")
In 3191, the crew of the USS Discovery learned from the clue left on Halem'no that they had to find Labyrinths of the Mind in order to get the next map piece. However, it was likely that no copies of the book existed anymore after eight hundred years, and they needed the original. With the help of Commander Jett Reno's knowledge of rare manuscripts and Cleveland Booker's empathic abilities, they were able to track the original to the Archive in the Badlands. (DIS: "Erigah")
According to the Archive's records, no one ever came looking for it before the arrival of Discovery. After touching the card on the inside of the book, Captain Michael Burnham was transported into the mindscape where she was tested by an AI left behind by Derex to see if whoever came looking for the Progenitors' technology was worthy of it. While Burnham was trapped in the mindscape, Commander Rayner searched through the book, but couldn't find any information that could lead to the location of the final map piece.
During Burnham's time in the mindscape, the AI read Labyrinths of the Mind while he was testing her, with the book at one point giving Burnham a clue as to the true nature of the mindscape. After Burnham passed the AI's test, he closed Labyrinths of the Mind and directed her to where the clue was hidden in a crystal in one of the viewing rooms. The AI also told Burnham a secret that she would need to know when Burnham arrived at her final destination. (DIS: "Labyrinths")