Catacombs are underground galleries used for burials.
Catacombs???
They were called the catacombs. They were the cemeteries of the Romans who converted to Christianity.
They hid in what is called the 'catacombs', which are underground burial places.
underground burial
An underground tomb or burial place beginning with cat is catacomb/s.
Assuming the burial is underground, then it is called an interment, or the body gets interred. The overall "ceremony" or rite is called a funeral.
The recommended burial depth for underground electrical conduit installations is typically 18 inches to 24 inches deep.
they are the gallery
The recommended burial depth for UF cable is typically 24 inches underground.
Grand Gallery
a burial chamber underground, usually in a graveyard or church.
The National Gallery.