The Nicaragua Canal?
Okay, it doesn’t yet exist. But had the Nicaraguan Post not made a mistake in issuing a certain stamp, it may well have been in place for a hundred years!
Although building is due to start shortly on a new canal linking the Pacific and Atlantic Oceans, if the Nicaraguan Postal authorities hadn’t produced a graphically-exaggerated stamp in 1900, the canal might have already been in existence for a hundred years.