Inner Planes
The Inner Planes is the name given by scholars to describe the collection of realms of existence that are closest to the plane in which Oberon resides.
Oberon itself is in the Prime Material Plane which sits in the very centre of existence, Surrounding it are the Shadowfell and the Feywild (separated from the Prime Material Plane by the Shadow Veil and the Green Veil respectively. All of these planes are linked directly not only to the four elemental planes (Air, Earth, Fire and Water) but also the elemental demiplanes (Magma, Ooze, Ash, Ice, Dust, Steam).
In each plane there are regions of 'instability' where the barriers between realms are weak. With the requisite knowledge the canny traveller can use regions to traverse between planes. However, even without these travel is still possible by using the Ethereal Plane.
The Inner Planes are often pictured as being discrete and adjacent to each other (see image below). There's no simple way to produce a two-dimensional representation of what is effectively a four-dimensional relationship. Suffice it to say that each of the inner planes simultaneously borders/intersects each other inner plane, including the Prime Material Plane.
