Armor of Invulnerability
Armor (Plate Armor), legendary, requires attunement · 2024 rules, SRD 5.2
You have Resistance to Bludgeoning, Piercing, and Slashing damage while you wear this armor. Metal Shell. You can take a Magic action to give yourself Immunity to Bludgeoning, Piercing, and Slashing damage for 10 minutes or until you are no longer wearing the armor. Once this property is used, it can't be used again until the next dawn.
Also in the 2014 rules (SRD 5.1).