It was found in Cage, but the geometry is in many levels
There are differences between PC and PS1, likely due the change in Quad triangulation
PC
Left side
It’s pretty easy to do. Found here by -o-, then posted here on Discord by hdc0
Apparently you can do it down at the bottom too… (clip)
Right side
It is quite hard, and probably requires either luck or a setup. Found by Cheftoad here
Here is another clip of Thermospore getting it
(isn’t there another pattern where you are facing diagonally towards the Door / Gem?)
PS1
Left side
When was this first found? It is in this Hypnoshark run (on JP), at least
(Paulmall said (1 , 2) on PS1 it might be easier on JP than US/EU, but this is very unconfirmed)
Right side
Here is a clip of limbus getting it, during the Quad triangulation saga.
When was this first found? Is it the same as right side on PC? I mean there is probably some difference due to the Quad triangulation change