Sliding doors are a common feature in urban locations like Utakata Castle, Fudo Castle, Negishi Pavillion, Honcho Shimoyashiki and a small storage room in Mokuami Fortress. These are simple doors which can be completely opened by pressing Triangle or be slightly opened to spy by lightly pressing Triangle.
A special stealth kill animation will play if the player kills an unsuspecting enemy from behind a door; This will completely destroy the door, same as slashing it. Another special steath kill animation will play if the player kills an unsuspecting enemy from the corner of an opened door, the same one as killing an unsuspecting enemy from the corner of a wall. Jumping into, ramming or pulling the door with the grapple hook will push it from its hinges, functionally destroying it, not to mention making a ruckus that may alert nearby NPCs.
A slightly open door will not conceal the player as a closed door does. If the player has their back to the wall of the door's corner, they will not be seen. If the are direcly in front of it, either standing or crouched, an enemy may become curious and try to investigate or instantly spot the player.
If any NPC spots a destroyed door, they will become alert.
Be careful when you use doors to hide from alert Yojimbos, they have a tendency to destroy doors while searching for enemies.