Ice houses were used to store ice in the days before the invention of refrigerators. They were perhaps a status-symbol to impress one’s guests by being able to offer them ice-creams in the summer. Be that as it may, Ice houses have been around for a long time and were often built as underground chambers close to the source of winter ice. Apparently during winter the ice was carved out from the river in rather larger cubes than those we would recognize today, taken to the Ice house and packed with straw as insulation. How it worked I don’t know, but it is said the ice remained frozen for many months.
This one is to be found in woodland on the Sherborne Estate in Gloucestershire, (National Trust property), and is easy to miss on your walk around the grounds if you are not expecting it.