Plate Armor of Etherealness
Source: Dungeon Master's Guide
Armor (Half Plate Armor or Plate Armor), Legendary (Requires Attunement)
While you’re wearing this armor, you can take a Magic action and use a command word to gain the effect of the Etherealness spell. The spell ends immediately if you remove the armor or take a Magic action to repeat the command word. This property of the armor can’t be used again until the next dawn.