Thoughts about Planes
by RobinAs to the World Mountain Volcano itself could well be like the unique Ol Doinyo Lengai volcano World Mountain was based upon.
The Magical effect however could have several options of breaking/touching the Prime Plane.
As to the Spirit Realm, Limbo and the Plane of Entropy all being mentioned here;
All the Planar images I have seen on Inner and Outer Planes are 2 dimensional, and this does not feel right.
Ok my take on this is a bit difficult but I try to explain, try to visualise this in front of you in miniature holographic images
I think this as 3 dimensional. First the Prime Plane is encircled by the four Elemental Planes placed like a D4 around it. this in total is enwrappen in the Ethereal Realm, which is breached by the infinit Plane of Limbo (originally near the Prime Plane, now due the magic/nuclear explosion of Blackmoor drawn closer (as canon describes) and in 1700BC by the Broken Lands disasater and the explosion of the Blackmoor devices on the young dormant World Mountain volcano reactivated and breaching the Planar borders between the Planes enabling a touch of the Spirit Realm Which was describes canon in the ethereal Realm I believe to remember.
Limbo is described by Bruce Heard as an finite/infinite moebius Ring shaped Plane
Limbo will in this 3d image be fully enveloped by the Spirit Realm in a similar, yet opposite pattern, enabling the "insides" of Limbo being pierced by a shard of the Astral Plane and another by a shard/spike of the Plane of Death.
This way we can have the Spirit Realm touching the Prime Plane, while having Limbo in its midst, yet also having the Plane of Death/Entropy also having contact whithout a direct contact to Limbo. The Fairy Realm might even be intertwined with the spirit realm in its chaotic shape enabling"fingers"of the Fairy realm touching the Prime Plane.
This would also explain why the Hakomon locations all seem to have some entropic link to the local sources of magic as the spike/shard could have branched off while touching the Prime Plane, being fed by the local magic and death/decay/disease and evil caused by the Radiance and powerhungry individuals.
Similarly I see the large Elemental areas(The Great Whirlpool, The arch of Fire) being touches of the Elemental Plane.
This might be a bit difficult, as all these Planes in a 3d shape would be difficult to lacate, yet we need to be 4th or even 5th dimensional (As goldbox set there are only 5 dimensions looking at each other opposite) so these might seem to fade through the Prime Plane one way or another.
As such it is very possible that The spirit Realm touches other Locations (Blackmoor for example; or what remains of it under water or as ruin) or
Just an weird mathmatical inter planar Idea,
I desire to create this main image in a 3d shape(real or digital and moving) yet need to find the nessesarry programs, equipment, help or if making it physical I need the materials..
Eitherway when finished I would inform yáll.