This photograph is a real treasure! Carnock was a mid 16th century elongated tower house situated near Airth in Stirling. The house was transformed in the 17th century when the battlements (which once went around the turrets - you can just see the continuous corbelling on the one nearest) were either removed or cut down in size. The roof was heightened and the fenestration regularised.
In 1941 Carnock was completely demolished and now only weeds mark the site.
Salvaged from the ruins, however, was its oak entrance door which can now be seen in the Smith Institute in Stirling. This door is extremely unusual in that it has what appears to be a 'cat flap'! A more realistic explanation is that it was an aperture for an iron gun.