Head to the southeast corner of the cemetery (just north of Ukuku Prairie). You’ll see five headstones. Using the clues from the book as noted above, here’s what you need to do, in this order:
Push the bottom-right grave down.
Push the bottom-left grave left.
Push the top-left grave up.
Push the top-center grave right.
Push the top-right grave up.
Tada! Cue that discovery music, because you just revealed a hidden staircase.