This is basically how houses in central Europe work. The walls and floors are built with masonry (bricks or concrete) and wrapped in a thick layer of insulation

This is basically how houses in central Europe work. The walls and floors are built with masonry (bricks or concrete) and wrapped in a thick layer of insulation. This results in a building with a very high thermal mass. The result is that it takes a long time for the inside of the building to change temperature. The other day we had a warm sunny spring day (5C / 40F), so I opened all the windows and did some spring cleaning. I set the thermostat to 16C as I didn't want the heating coming on while I was doing this. I forgot about this, and the next day when I woke up wondered why the temperature in the house was only 20.5C (68F) as usually we have it set to 22C (72F) - then I remembered I effectively turned off the heating 18 hours ago, and forgot to turn it back on.