Focus Fire Governing Stone which shoots a ray of fire. Breaking, Arcing and Duration Tuning Stones means the fire jumps to more enemies, destroys enemy Barriers and increases the duration it does all this for.
If you have more than one stack of the Zoltun's Warding buff left at the end of a Vault then you'll be rewarded with a Wardwoven Chest if you have 4 stacks you'll get a Rare Wardwoven Chest too.
Typically Vaults end in what is informally referred to as a 'death room' or a 'danger room' where everything is being thrown at you — all the traps from the vault accumulated in one large room.