You are actually looking at the inside of a ruined building from the former Inchydoney manor, the wall on the left has obviously been quarried for other purposes. The quality of the stonework is impressive, still standing high after almost four centuries, but it must have been quite dark inside.
Those people were really craftsman with stone. I am impressed when I have been to Europe and see the bridges and buildings that are centuries old and much of our infrastructure built following WWII is falling apart.