The rune lock

  1. Find a sealed dungeon and step inside the antechamber.
  2. Right-click every Rune Block to light it.
  3. When all runes glow at once, the Aether Seal dissolves and the vault opens.

Inside

Past the seal wait monster spawners and a loot chest. The fight and the reward are the point — clear the room, claim the chest, and move on.