Fourteen-year-old Lena knew almost every crevice of the cliffs above Vulture Bay. After a night storm, she set off for the beach, searching for treasures thrown up by the waves. A seagull screamed overhead, the wind smelled of salt and the rust of wet railings. Among the branches and seaweed flashed a bottle with a copper stopper, quite heavy. Lena popped the cork with a penknife and slid out a foil-wrapped roll. Inside buzzed a rusty key and a thin tin with a lantern sign. Three triangles and the date were engraved on the tin: tomorrow's foggy morning. Iwo, Lena's cousin, knew every current and humour of the old lighthouse. He came running when she called, and looked at the find with a furrowed brow. "The three triangles are the Three Blades cliff," he said, showing the map on his phone. "And tomorrow morning means the low tide, the biggest in a month, will reveal the threshold of the tunnels." On a sheet of film, someone added with a pen: "Before the fog returns, find the entrance." Under the lower stairs of the lighthouse hung a padlock that no one remembered anymore. They took the torches, the cord, a supply of batteries and a small drone with a camera in a cowl. The tide revealed a slippery sill, and the waves oozed lower, as if with reluctance. Lena pushed back the ivy and came upon a narrow door, almost innate in the wall. The key from the beach popped in the lock and clicked for the first time in a long time. Behind the door, a chill and oil breezed in and the corridor sloped down towards the rocks. Someone had left a chalk arrow and a short sign on the wall: "Deeper". The further they walked, the more the earthy drumming rumbled underfoot, resembling breathing. Torches flashed on the wet cables and the walls flashed with crystals, like the night sky. A drone flew ahead and showed an alcove with a trellis over black water. In the corner stood a metal cabinet with a sign of three triangles and a lock. Lena slid the key in and the mechanism clattered, as if waking up after years. Somewhere behind them, water crackled, and then in the darkness someone whispered her name. Iwo froze, and the drone light hovered over the grating, a trembling, milky point. A second light came from the tunnel opposite, moving in a strangely slow rhythm.