You find yourself with a friend on a completely deserted (devoid of objects or people) and flat plane. The only thing of note is a wide river; you can just manage to see the other side of it. There is a straight metallic bridge to the other side. It is held only by 2 poles on each side of the river, and is built extremely high over the river. You can not climb up a pole, and walk across the bridge.
You have a single metal pole of approximately $1$ foot length with you, and a rope of at least $10$ feet length. You, however, do not know the measurements. You have absolutely nothing else with you that can be used (no measuring tapes, ladders, stopwatches, airplanes, kites, and so on). You can not use your clothes as a device, and you have no idea where you have been located (you may not even be on the Earth).
Find out approximately how wide the river is, in terms of the rod given to you?
So the answer would be something like
River width = 55 rods.