Many people have seen and enjoyed the movie "The Princess Bride". In the movie as Wesley and Buttercup are traversing the fire swamp when the duo encounters the ROUS's, but do rodents of unusual size exist in the real world. "Inconceivable!", you say, well possibly they do.
An article in the Mirror may change your mind that ROUS's do exist in England near a kid's playground no less. The picture of the dead rat was posted to Twitter and it went viral.
It is not as gigantic as the ROUS's in the movie, however the pictured rodent would certainly look enormous to a kid.
It is worth mentioning that comments to the article and other articles have been written which demonstrate how the use of force perspective can make objects appear larger than they actually are in real life. So maybe the existence of rodents of unusual size is inconceivable and just the stuff of story tales.