There was the two 500 foot deep shafts they discovered in Knightswood. Nobody was harmed but terrifying to think about. In a lot of cases, these deep shafts were plugged with railway sleepers and logs then covered over. Over time, the wood rots away and the shaft collar collapses. https://www.heraldscotland.com/news/13060651.disused-mineshaft-works-extended/