Complex sentence: In the late 1500s Dunimarle Castle had a coal mine in operation run by Sir George Bruce, the mine had a tunnel that led down to the nearby River Forth, which is some 30 meters below so that the coal could be loaded onto ships.
Split into simpler sentences: In the late 1500s Dunimarle Castle had a coal mine in operation run by Sir George Bruce. The mine had a tunnel that led down to the nearby River Forth, which is some 30 meters below, this was so that the coal could be loaded onto ships.