Mysterious thing

You’ll never guess what it is and why it’s here if you don’t study the sections of this website about KaUR, the Salpa line and the like. This thing is for firing a light or heavy machine gun while sitting on a rotating bicycle seat mounted on the back wall of a concrete block. The machine gun on the turret was attached to the frame on top of the block. And a big stone here instead of a parapet. Simple and inexpensive...