Information Sign for the Grand Coulee Dam
This is a fairly old sign, so I am not sure if it is still accurate concerning the Grand Coulee Dam being the large concrete structure in the world. The most interesting part of this sign to me is the newspaper article in the lower right corner. You cannot read what it says, but you may be able to make out some of what is in the drawing. It claims that the drawings consist of in scale drawings of some famous large things to compare with the Grand Coulee Dam (which dwarfs them all).
Location: Crown Point Vista, near Grand Coulee Dam, Washington