What do I do at the Altar?

Hint 1 of 9:

This is Apollo's temple.  What have you learned about Apollo?

Hint 2 of 9:

Have you read the scroll you found in the Octagon room?

Hint 3 of 9:

Apollo loves music.

Hint 4 of 9:

Have you found the Pan pipes?

Hint 5 of 9:

Play them.