In particular, the book of Genesis.
Some have tried to nuance their interpretation of Genesis (in an attempt to reconcile it with "science," especially evolution) -- but if Christianity and Christian faith is grounded in a historical narrative, salvation history, i.e. what God has done for mankind, then how can one "mythologize" certain books without undermining Christian faith? Contrary to what some Roman Catholics think (perhaps subconsciously under the influence of some exaggerated form of scholasticism), Christianity is not a set of abstract theological propositions which do not need the background of a historical narrative; rather our knowledge of God is through His actions, especially those directed to mankind.
