Is There a "Triangle" Type Opening in Astral Projection?

So I was talking to this LaKota Indian once, and he had this necklace with a triangle on it.... I asked him what it meant, he grabbed it and said " Ive been there".

So is this an actual place, or is it some sort of port hole, and why is it a triangle shape?

Ive noticed this in a few more places, like that Talking Heads video "And She Was".