My grandparents were people of walking and bus rides. They did not trust traveling underground. The few times I traveled with them on the subway, they appeared tense: a fall, a shove, a robbery. In a way, wherever the sun did not shine was always territory for the unexpected, the dangerous, and the hidden. Insects lived underground. Worms, the dead, ownerless treasures, evidence of unsolved crimes. Also purely practical aspects like the fact that it was not safe. The ceiling could collapse. What happens if you get trapped in a tunnel, if the train doors close before you. And not to mention the stifling heat or the excessive gathering of unknown people, their smells.