Yeah maybe it hints it is in the water hanging under the bridge or off the side of or under one of the boat docks. I don't get the phrase "but this invention, is not a toy". It might be referring to the name of something that is or was the name of a popular toy? Bridge name, boat name, machinery name, trail name, the boat house on the dock?
"Where the bells toll" probably refers to a bridge which is from the movie "from whom the bell tolls" in which the movie revolves around a steel bridge.
The river in that movie/book by Hemingway was based on story about the bridge built across the " Rio Guadalevin" river. There's possibly your "Rio" part on the map, along with the bridge reference tie in again.