It's a house -- and a garage! -- built into the base of a cliff. These structures occupy a fenced-off area, marked by ominous-sounding warning signs about any motor-vehicle use behind those demarcations demanding special permits. I suspect the residents (Bond villains? Retired Hobbits?) have filled out the necessary paperwork.
While stopping to snap this photo, I had ample time for other wondering, such as: How dark is it in there? Is the visible chimney the only ventilation? What about water and electricity -- how on or off the grid is this pseudo-bunker?
All of these queries will remain unanswered because, as I mentioned, this is somebody else's life, and I was just pedaling through.