The world’s largest public toilet is (or maybe the largest plot of land for a single toilet) is a 200-sq meter plot of land in Ichihara City, Japan.
(It cost ¥10 million and was installed for tourists to the area, but the loo is in a transparent booth! It’s boxed in glass, in the middle of a spacious garden of potted flowers and plants surrounded by a two-meter-high fence, with spy satellites and Google Earth, who on earth would use it?)