This is the 3rd "test" of 5 on the infamous Pilgrim's Path, and in order to pass, I must open the rock-door. Unlike other gates of its kind, there is seemingly no lever or pull-chain that raises it. So, I must believe that the statue of Nocturnal is in some way important. Also, it would seam that the journal of a failed explorer holds a riddle relating to this very test.
"Offer what she desires most, but reject the material. For her greatest want is that which cannot be seen, felt, or carried"
Help a poor Nightingale out?