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.