The huge chimney can't work as it has no connection to the ovens inside. It was built, apparently around l947-8 by former inmates and intentionally built so massive in order to get visitors into a horror atmosphere.
When Ditlieb Felderer put the lie on the officials of Auschwitz while talking to them, they promised they would change, and inform the people it is faked. That was in the l970's. Today, in soon 2009, they still haven't stopped lying, and continue to lie to the visitors, making them believe it is authentic.