i think i now were you r on about right you run towards the ledge then press x (i believe)and dante should jump over to the other side then you go through the doors and then continue on through the door and after a couple of doors and a little climbing you face phantom once you kill him you go through the gap and pic up the tridant and drop down the hole and go round the back of the big mechanism and pic uop the granade launcher and then you go back to the other side to bash the glowing thing which lowers/rises the gate can't rember then you go back to the other side and drop down the new opeing in the ground the room should look familier then you you oplace the trident in the mentel at the end and run like hell to the room below you were you had to climb that contains the big gate and hopefully you should make it in time to pass through the gate and get out of the castle and continue the game
hope that helps