After walking down two floors, I realized that it was very dark down there, because the street lamps on the first floor were installed so low that a taller person could touch them with a single reach, so some people with no sense of public decency often unscrewed the bulbs and took them back to their own homes, and the first floor was often dark. I cursed and continued down the hall. After walking down another floor, the surroundings became darker and darker, but I was surprised. Because I didn't go to the exit of the first floor, there were actually stairs below!