The Vault is a special location which appears in Dragon Quest III, Dragon Quest IV and Dragon Quest V. It is a place where the player can store gold and items to be retrieved at a later time. It was removed in Dragon Quest VI (and remakes of some of the older games) in favor of using a bank and The Bag.
Dragon Quest III
In Dragon Quest III, the vault is located in the town of Aliahan in the same building as Ruida's Tavern. The item portion of the vault does not accept rare items. It also charges a calculated amount of gold to retrieve other items which are stored there. This cost is based on item value. One particularly common item to be stored in the NES version is the Golden Claw, as it causes repeated enemy encounters when in the possession of the player. However, it is quite expensive to retrieve after being stored.
Dragon Quest IV
In Dragon Quest IV, the vault is available only in chapter 5. Torneko's wife runs the vault in the town of Endor. Unlike Dragon Quest III, removing stored items from the vault does not cost anything and rare items can be stored.