I think I read somewhere that at the Ypres battlefield there are underground piles of explosives that were meant to be exploded along the German line, that were placed there by sappers during the war, and never detonated or removed. Back in the 1950s one of caches detonated due to a lightning strike, and it was a huge explosion. There still one other cache that they know about.
Speaking of Ypres, have you watched the movie “The Wipers Times” (2013)? Great movie!