Stone Door

Summary
Stone Doors are the highest tier of door in game. Stone is impervious to fire, but can easily be destroyed by grenades or other artillery items. Climbing picks can be used to climb up a stone door. As a door or trapdoor, stone doors have 8,000 health. When used as a shutter for a window, they have 6,000 health.

Building/Configuring
Stone doors have three types that can be placed. Unlike other building blueprints, the stone door type depends on the shape of the wall or ceiling into which it's placed. They will automatically select the right type when held over a compatible spot.Doors can also have pin codes or admin locks placed on them, like storage chests.
 * Door
 * Window Shutter
 * Trapdoor/Hatch

Required Skill Trees/Skill Points
Stone structures are unlocked with the Esotery of Building skill, at the very end of the Construction and Mercantilism skill tree. 25 skill points are required to unlock them, and they must be crafted in a smithy.