Hidden Lines and the Break

The air at the bottom of the tower was damp and cold.

Ryan crouched steadily beside the crack in the stone, pressed close to the wall as he used his fingertips to feel the minute vibrations on its surface. He closed his eyes and adjusted his breathing, focusing his hearing, sense of touch, and balance entirely on his body's perceptions. The tower's vibration patterns, the echoes of mechanisms in the main passage, the scraping of the metal framework deep within... He pieced these details together bit by bit, forming an impression of the tower's structure.

He opened his eyes, his gaze calm.

In front of him was a crack almost completely concealed by dust. The wall bricks had already loosened, and thin fissures wound downward, spreading like a spiderweb around the area. He lowered himself and gently tapped with the handle of his short knife, again and again, slowly determining the weakest section.

The tapping echoed faintly through the silence, accompanied by the calculations running constantly through his mind: the thickness, the vibration frequency, the size of the cavity behind it, and whether it could bear his weight.

At last, he found the spot.

He drew a deep breath and carefully pried at the stones with both hands, loosening them bit by bit. Gravel slid down with a faint rustle. He kept his breathing low the entire time, afraid of triggering structural resonance deeper inside the tower.

About ten minutes later, a crack just wide enough for a person to squeeze through sideways appeared.

Ryan hung his backpack in front of his chest, lowered his center of gravity, and edged into the narrow passage step by step. It was completely dark inside. He could only feel along the wall with one hand while keeping the other pressed ahead of him