The beginning of a mind-melting puzzle.
The Conspicuous Note, before use.
The Conspicuous Note is found at [51, 59] on the side of the Heart of Darkness, accessible from the top. It holds the first clue for obtaining 
[Baa'ls Darksign]. See Riddle of Baa'l for more information and the whole list.
Contents
Conspicuous Note
Begin at the beginning.
Solution
The beginning refers to the place where it all began, the map in Drak'thul's camp in the Broken Shore. This is where you will find... an Ordinary Pebble.
Patch changes
Patch 8.0.1 (2018-07-17): Added.