Northeast of Montreal. The Quebec City bridge. You carry a pilot on the ship between Montreal and Quebec on the St. Lawrence River and ours asked if I'd ever seen a bridge that you can go over and under at the same time. I said no, and he instructed me to turn on the fathometer. You really need a recording fathometer, or a fishfinder with bottom contour I suppose, to get the full effect. As you pass under the Quebec City bridge you see a mirror image of what you're seeing overhead on the fathometer.
Quebec Bridge - Wikipedia, the free encyclopedia