Signe maps caves.
Not for tourism or science. For the record. The national survey pays her to descend, measure, note, and return with a description precise enough that someone who has never been underground could find their way to any chamber she's catalogued. The work requires a particular temperament: comfort with darkness, patience with repetition, faith in notation.
Her current assignment is a system in the eastern hills. Limestone. Old water channels, mostly dry. The caves have been visited before — there are chalk marks on some walls, a few bolts drilled into ceilings — but never formally surveyed. She is the first to draw the map.
She begins at the entrance and works inward. Each chamber gets a number, a description, and a set of measurements: length, width, ceiling height, compass bearings of every passage leading out. She records the texture of the walls (smooth, fluted, fractured), the presence or absence of water, the color of the stone. Her descriptions are dense and specific. Chamber 4: "Irregular oval, 8m x 5m, ceiling 3.2m. Walls fluted, light grey with rust banding at 1.5m. Two passages: NNW (1.2m wide, descending) and ESE (0.8m, level). Floor damp. No formations."
By day three she has catalogued eleven chambers. The map is clean. Passages connect in ways that make spatial sense — she can trace a path from the entrance to any numbered room and trust that the distances and bearings would bring her there.
On day four she finds chamber twelve, and the trouble begins.
Twelve is reached through a passage from seven that she hadn't noticed before — a gap behind a pillar she'd used as a reference point. It opens into a room she's certain she hasn't seen. But the room matches her notes for chamber three. Same dimensions, within measurement error. Same wall texture. Same two passages leading out. She checks her compass. The bearings are different. It's a different room. It has to be. But the description she wrote for three would serve for twelve without changing a word.
She writes a new description for twelve, trying to find the distinguishing detail. There's a faint watermark on the east wall. Was there one in three? She checks her notes. She didn't record one. That might mean three has no watermark. Or it might mean she didn't notice it.
She goes back to three.
Three has a watermark. Fainter than twelve's, or the same — she can't tell whether she's comparing the marks or comparing her memory of twelve's mark to the reality of three's. She adds the watermark to three's description. Now the two entries are different. But the difference is one she didn't see before, which means her original description of three was incomplete, which means every other description might be incomplete in ways she can't check from inside the rooms she hasn't revisited.
She revisits them. Chambers one through eleven, over two days. She finds things she missed: a narrow fissure in five, a discoloration in the ceiling of nine, a sound in two she hadn't noted — dripping, faint, possibly from an adjacent passage she hasn't found. Each revision makes the entry more accurate. Each revision also means the previous version was less accurate than she'd believed.
By the end of the week she has fifteen chambers and a map that is simultaneously more detailed and less trustworthy than the one she had on day three. The eleven-chamber map was wrong in ways she couldn't see because the errors looked like facts. The fifteen-chamber map is right in ways she can't verify because the corrections were prompted by finding twelve — and twelve might have primed her to see watermarks everywhere, or fissures, or sounds.
Her supervisor calls. How's the survey?
"The cave is larger than expected," she says.
"Good. How much longer?"
She looks at the map. Every room she enters makes two others uncertain. She can't go back to the version of herself that found chamber three and didn't notice the watermark. That Signe is a different surveyor. Her notes are from another expedition.
"I'm not sure," she says.
She descends again in the morning. There's a passage from fifteen she hasn't taken. She clips her light to her helmet. She checks her notebook. She enters the passage.