It must be France

Found in a collection of other cards of varying age, this one which has the bottom left corner snipped off.  The card has never been written, no postmark, but I'm going to hazard a guess that it dates from World War I and that the corner has been snipped off to avoid censorship - or maybe even the result of censorship.

I've tried to locate the "Jardin Public - Le Cascade" but so far no success.  Both Cambrai and St Omer have had postcards showing their public gardens with waterfalls but none exactly the same that I can find.  There was a large-scale tank battle at Cambrai in 1917, but St Omer was the base for Royal Flying Corps for the fours years of the war, so it seems more likely.