When you make it past the sequence fans, you have to pull the switch in between the fans and open the door. Kill the two vamps that come for you. One of them is killed to save a guy so don't forget to go up to him and talk to him and he will give you a holy vial. After that there is a big hole, but don't jump it you will fall and die. Look over to your right and you will see a skinnier pipe than the others. Jump to it and shimmy across and you will have made a safe way across!