The Zephon boss battle changes during development and is somewhat different in the alpha and beta builds. In some builds Zephon is presented as a revived vampire, complete with sparkling effect. Notably in both alpha and betas there are two side chambers which lead upwards and curve back toward the main chamber. In the early alphas these are open and curve back to give a view of Zephon's side. In later alphas these corridors are shortened and blocked with permeable barriers and organic spouts are added which provide souls for Raziel to consume. This mechanic survives into beta versions where Zephons legs can attack you in the side chambers. Ultimately the chambers were removed for retail.
Several further rooms can be found from a passage behind Zephon's head. These are of unclear purpose but may have been attempts to build towards the Pinnacle of the Cathedral