Gas chamber in a dream: what does it mean?
There is no symbolic reading of this that would not be an insult. It is a historical fact, and a dream about it is almost always about knowing that.
How do the four traditions read it?
Each reading below comes from a named tradition and a cited source, so you can see where it came from and decide what fits your dream. The four often disagree, and that is the point: a symbol rarely means one fixed thing, and the distance between Freud, Jung, modern research and myth tells you more than any single verdict could.
Freud
Freud died in 1939, having left Vienna the year before, and four of his sisters were murdered in the camps. That is the relevant fact about reading him on this, and it is more useful than any interpretive framework he left.
After Freud, The Interpretation of Dreams (Brill trans., 1913), public domain.Jung
For Jung a dream about an atrocity is usually about the dreamer's relationship to knowledge of it rather than about the event, and the horror reported tends to attach to comprehension rather than to threat.
Our summary of a Jungian reading, in our own words, not Jung's. See Jung, ed., Man and His Symbols (1964).Modern
Under the continuity view these tend to follow education, documentary, museum visits and family history, and they are reported particularly by descendants of survivors. For anyone with a family relationship to this, the dream is inheritance rather than symbol and belongs with a person.
Our summary of the continuity hypothesis, named by Calvin Hall and Vernon Nordby, The Individual and His Dreams (1972). Its correct scope is disputed; see Domhoff (2017) and the replies to him.Mythological
This is documented history rather than folklore and is treated as such here. Traditions of purification and of mass death do not illuminate it, and reaching for them would be a category error with a particular kind of offence attached.
Rosmerta Publishing editorial synthesis (after Brewer).How can writers use this symbol?
The same symbol, read as craft material rather than as a dream. What it does on the page, how genres use it differently, and what happens when you turn it inside out. Written for novelists, screenwriters and poets who need the symbol to actually work, and it ends with something to try.
In literature
The literature is enormous, largely written by survivors, and the central argument within it is about whether the subject can be fictionalised at all. That argument should be read before anybody adds to the pile.
Rosmerta Publishing editorial synthesis. Our own words; no quoted text.What it does in a story
It is not a device and cannot be used as one. Any story invoking it takes on an obligation of accuracy that most fiction is not prepared to meet.
Genre conventions
Testimony is the primary form and is where a writer should start. Historical fiction that works is meticulous and small in scope. Anything that uses it for atmosphere fails immediately and visibly.
How to subvert it
Do not write it as a scene. Write the grandchild finding a document, and the afternoon that follows.
Try this
Write a museum room from the point of view of a guide who does this every day. Four hundred words.
Only the first of these names a source. What a symbol does in a story, how genres treat it, how to invert it and what to try are our editorial judgement as writers and editors, not findings from a body of research. They are offered as craft opinion and should be argued with.