The Corner Battlements Pack is part of the Castle Builder System. It is made of "Dwarvenite". This item was initially available as an add-on to a pledge level during the Castle Builder System Kickstarter. The item comes in both painted and unpainted versions.
The Corner Battlements Pack comes with these 5 pieces:
(3) Corner Battlement
(1) Corner Battlement w Trapdoor
(1) Reinforced Lattice Trapdoor