I found the second piece of the Trismegistus! (no spoilers)

[Hguols]

I'll do my best to shed some light....

The orb is only on the light perspective. Do you remember where you found the "earthen key"? You had to <b>unearth</b> it from a designated spot kind towards the back of the "castle" - in the dark perspective mind you.

That same spot in the light perspective, you can <b>unearth</b> a feather jump spot. From there you can jump and gain access an otherwise unreachable area and the orb will be there.... assuming you touched it the first time.