Here's a big one: Do you have the technical skill or know someone who has? I live in Paris. In the halls of the metro station underground at Duroc station, I was walking behind a hand-in-hand couple who were blind. They talked endlessly and tapped tapped tapped along. The corridor turned off to the left. The couple followed along in the middle, like not even thinking about it - with the curve. How did they know that? Ahh! because they heard it turn. They had not tapped the wall, they...