Montag compares his bedroom to a mausoleum. What does that symbolize?

The word “mausoleum” refers to a place where a corpse is kept. In context, this word is used in conjunction with a description of Mildred lying “like a body displayed on the lid.” This is where we see that Mildred isolates herself from the world feeling that the things around her are dead; she, in fact has chosen death but won't get her wish.