What is a name of a room under a church?

Answer 1

For Catholics and other Liturgical churches the religious items are kept in a Sacristy. Other groups just call it a closet or storage room.

Answer 2

A common name for a room under a church is a basement or a crypt. Crypts are often used for burials or storing religious artifacts.

Answer 3

It is called an Attic

Answer 4

a crypt

Answer 5

Churches, synagogues and some kinds of temples have a room that is typically called the sanctuary. That is the main hall used for large worship services. Large churches and large synagogues sometimes have smaller rooms used for worship when the main sanctuary is way too big for the number of people in the congregation. A common word for those smaller rooms is a chapel. In some Christian denominations, churches are distinguished by having relics or saints or other special items that allow full status as a church. Smaller worship halls in those denominations are sometimes called chapels. Similarly, many institutions such as hospitals and universities have chapels, which are worship spaces that are not necessarily associated with any one denomination.

It seems that mosques usually refer to their main room for worship as a prayer hall when it is described in English.