The area in Cornwall, England where this mine shaft opened up is known for it's extensive mining history. This house used to be a location that was mined for tin, or maybe copper before the mine shafts in the area were filled in and it became a neighborhood. Stuart Dann, a mining expert in the area told The Daily Mail that no one knows about the mine shafts that used to be in the area until they check a very old map:
It is easy to see the woods, fields and houses and assume nothing was there. If you go back to 1750, the area was completely different - there were dozens of engine houses and hundreds of shafts in the area, which probably looked a bit like a desert.
As mines closed, many put very large bits of timber across shafts and backfilled them, thinking this would be safe. Gradually all evidence of the engine houses and covered shafts went and we and builders before us assumed there was nothing there - apart from on the old maps of course.The old maps often clearly detail the layout of various mines and where shafts are. It is these maps which mean the difference between buying a house which might fall down a hole, or one which sits on firm ground.
Thankfully, this mine shaft opened during a survey of the house before it was put up for sale. The house may never be able to be sold now, half the garage and the patio have disappeared down the mine shaft and surveyors are worried about the permanent damaged to the house.