Planes and layers

[Tiiba]

I don't understand what layers are. To get to another plane, you need Plane Shift or Gate. Within them, you use Dimension Door, Teleport and its bigger variants, or feet, if you're a muggle. But what about layers of a plane? Can you teleport from one to another? How far are you considered to have moved? Can you walk or swim or fly there? What does it look like when you reach a threshold?

[Icewraith]

I was under the impression that any particular level of hell or layer of the abyss, for instance, was a valid target for Plane Shift when on the Material Plane.

Once you're there, though, you're stuck using the Plane of Infinite Portals, the Styx, the Infinite Staircase (if it exists in the setting), or finding pre-existing portals to travel between Planes. At least, that's what I gather from the line "the creatures need to find other means if they are to travel back". All that nonsense is rendered moot once you can Gate as long as you're not hanging out in a deity's territory.

Also with linked planes, if you wander far enough in a certain direction you'll often blunder into the next plane, but it doesn't seem like you can teleport to one. You definitely get areas like that in the Elemental planes, where particularly hot water may actually be a signal you're approaching the Elemental Plane of Fire, for instance. The description of a plane usually indicates which planes you can travel to from that plane and how much effort it takes to get there.

[Solophoenix]

The line about needing another method to return just means that you can't return on the casting of Plane Shift that got you there, ie, it's not a continuous effect holding you on the plane, that you can dismiss and poof home. Another casting of Plane Shift will be absolutely fine for further planar travel.