Inside the clock tower

From the street, the tower had looked narrow but harmless, and I had volunteered to carry the notebook because the climb sounded simple. Inside, the stone staircase wound upwards so tightly that I could see only the next three steps. After the first turn, the cheerful voices from the street disappeared, and I became conscious of the walls pressing close on either side. The steps had been worn into shallow curves by people who had climbed them long before me. Thinking of all those earlier visitors made the tower seem less like an ordinary building and more like something I had been briefly permitted to enter. At the first landing, I stopped to catch my breath. A thin strip of daylight showed beneath the door above, and the wish to discover what was beyond it began to outweigh my unease.

In your own words, explain the writer's thoughts and feelings at the start of the visit to the tower.