Can't seem to find my way in to the naga area to complete my mission to kill it. Please help! Is there a skull lock or switch I am just not seeing? Thanks.

after summoning the naga spirit at the serpant head statue and answering her questions the mouth opens and you can walk in. now save the game i repeat now save the game. press the button in front of you and you should drop into circular chamber (4 times i found myself in an enterace to a passageway that i could not get out of, in frustation the next time i reloaded i pressed the button twice and dropped through). only one way out of circular chamber into another with two closed doors the naga enters through one of the doors soon after you enter.