Thmyl Fysbwk Layt: Andrwyd 2.3.6

But if it's Atbash (A↔Z, B↔Y, etc.): t (20) ↔ g (7), h (8) ↔ s (19), m (13) ↔ n (14), y (25) ↔ b (2), l (12) ↔ o (15) → gsnbo — no. Given the puzzle-like nature and the numbers 2.3.6 , it might be a book cipher — page 2, line 3, word 6 of some text. Or a software version "Andrwyd 2.3.6" (Android misspelled?).

Then she remembered: Andrwyd . Not a typo for Android. It was the name of a dead drop — an old weather station near the Arctic circle, decommissioned in 2015. And 2.3.6 were the coordinates: 2 km east, 3 km north, depth 6 meters. thmyl fysbwk layt andrwyd 2.3.6

Actually — I notice "thmyl" if each letter is shifted one forward in alphabet: t→u , h→i , m→n , y→z , l→m → uinzm — nonsense. But if it's Atbash (A↔Z, B↔Y, etc