The inner sanctum is evil, especially the part with the big rotating mold bar and the keys. Had fun though.
well first you need to find 2 secret artifacts and then to go the hole on the left wall past the doors then do some extremely hard jet platforming
(spoiler below)
first one is at the bottom left main door artifact. You need to get to the grass area and get in the hole on the left wall
second one is in a hole at the top of one of the temples you use to unlock things (I think it was the moving water clouds one)
then you go to the shortcut unlock in the door temple and go up the small water fountains then jump off to he side on the last one to get in.
the rest is up to you, your skill and your persistence.