I'd no idea as to what this was or had been. Maybe an old mining entrance in the side of the mountain. Or perhaps a water outlet at some time or another.
{I reckon Happyman will know though}
I thought it might have even been a kiln, but there were no signs of heat, or smoke damage etc to the bricks.
It was an interesting looking piece of construction.
The scenery in general was magnificent.
We certainly have a very beautiful country.