There are several keyholes found throughout the island and its unique, ever-changing landscape that you can peek through to get a glimpse at the truth behind the boy's visit on the island. They are stone pillars about the boy's height with a golden keyhole shining light out of it. The video, provided by Somewhat Awesome Games, highlights where these are found, and I will go one step further to help narrow down the timestamps and the chapters that they are located in. They will only be found within the first four chapters, so if you have missed one and you've completed the fourth chapter, do not fret; there is a Chapter Select option after completing the game so you can go back and collect the others, along with performing other actions, should you need to.
Chapter 1:Keyhole #1: 0:06 - 1:31
Chapter 2:Keyhole #2: 1:35 - 2:00
Keyhole #3: 2:02 - 2:37
Chapter 3:Keyhole #4: 2:39 - 3:30
Keyhole #5: 3:35 - 4:24
Keyhole #6: 4:27 - 5:48
Chapter 4:Keyhole #7: 5:54 - 6:40
Keyhole #8: 6:49 - 7:31