While modifying base concepts for my own personal campaign back in the early 2000's, I thought about the planes as written in the various WotC products of the time. It occurred to me, that many of the off-prime areas, including the inner and outer planes, could be represented with a concept of planets, and extra-dimensional planet-like places with different physics. I then wrapped that idea around a new cosmology and planes concept, which brought a lot of the Planescape concepts into a new rules set for my campaign.
Bringing my particular extra-planar module to NWN, containing the city of Dark's Gate, requires that I bring at least some of that other-world magic to NWN, and I may have to settle for skyboxes for much of it.
What skyboxes have you come up with to represent your extra-planar areas? Especially those of Gehenna, The Plane of Shadow, Baator, Bytopia, and Hades.
For one of my lower planes, I imagine a spherical world with the inside blown out into space. The demonic inhabitants live not just on the outside, but the remains of the inside, and floating innards. From the perspective of those living within, you can look up and all around to see the shell of the world with various clouds and rock fragments floating freely. I think this could be easily represented with a good skybox, much like the PS:Torment video showed the torus world of Sigil, with its overhead cityscape.