Do you know what ice houses, succession houses and ha has are? They are all structures often found in the grounds of stately homes in Georgian times – and later. All three are mentioned in The Mrs MacKinnons, and there were a few ‘what does that mean?’ comments from people who read the manuscript in development.
Ice houses were used to store ice from frozen lakes or streams in the winter, keeping it cool enough for it to be used the following summer. Some were below ground; the ones that were not were often covered with a thick layer of earth for extra insulation. All you would see from the outside would be a wooden door.
UPDATE: An ice house has been discovered beneath a Georgian house in London. Here’s a link to the Guardian article on it.