After the Leap of Faith episode, you have a few episodes to finish before unlocking this achievement: Full Spectrum I, Full Spectrum II, and Hold On To Your Belief.
A Full Spectrum I
Follow the path until you get to a big open room with crystals. On the right side of the central crystal is a pillar with another word puzzle. The answer is "I AM THE LIGHT WHO FOLLOWS ME. I WILL NEVER WALK IN DARKNESS. BUT WILL HAVE THE LIGHT OF LIFE." This shines a yellow light down. Head to the back of the room and climb up the white ledge. Platform and grapple your way up to a switch to pull. This shines a blue light down. Continue platforming and grappling to the last switch which shines a red light down. Zipline down and drag the crystal head to the white beam and move it until all three coloured beams are hitting the right crystal. Head through the newly opened doorway to a door with another magic square puzzle. The answer, from left to right, top to bottom, is VIII, VII, II, I, II, VII, I. Head through the door to finish the episode.
A Full Spectrum II
This episode is entirely following a linear walkway and some platforming. Follow it all the way to the end to finish the episode.
Hold On To Your Belief
Follow the path until you get to what looks like a puzzle. Go over to the tree to find another pillar with a word puzzle. The answer is "THE WIND BLOWS WHERE IT WILL. AND YOU HEAR ITS SOUND. SO IT IS WITH ALL BORN OF THE SPIRIT." This causes steam to come out of the ground. Drag the three carts onto the correct steam pipes (they will start moving from the steam when placed correctly) to open the door. Go through and follow the path until you get to a pedestal on a cage in a river. Go instead and you'll find all the remaining puzzle pieces together here. Take them, then platform and climb your way out and through the cave to end the episode and unlock the achievement.
Guide taken from XA.