Do you mean Visitazione's Secret? If so, this link shows you where the entrance is and how to do it. http://www.youtube.com/watch?v=kJkDQvVI7Cs But I did the tombs in a random order. So if that's not it I apologise.
Believe me..I know how you feel. Youtube is great, but I could not find them all on there. Well maybe you can, but I ran across this site: http://thehiddenblade.com/ When I was playing. Just search up the secret tomb you want and it'll have a step by step video walk through of them entire tomb, and each secret. I was able to make it pretty smooth by using that site.