When I went to Auschwitz earlier this summer, I saw for myself that the supposed gas chambers were built RIGHT NEXT TO THE GUARD BARRACKS.
And yes, I got to see the internet-infamous wooden gas chamber door that locks from the inside and has a window on it. https://blossom.primal.net/069f31b276ca72d9b3187ee110a5eb49e844dbf56f24c6af42fe659289dd2e00.3gp