Sacristy

A sacristy, also known as a vestry or preparation room, is a room in Christian churches for the keeping of vestments and other church furnishings, sacred vessels, and parish records.
In most older churches, a sacristy is near a side altar, or more usually behind or on a side of the main altar. The sacristy is also where the priest and attendants vest and prepare before the service. They will return there at the end of the service to remove their vestments and put away any of the vessels used during the service. The altar linens are stored there as well.