Tech level's already been locked in at Renaissance. You might get a flyer A La Da Vinci's notes, but modern-style jets won't be in there.
Tech level's locked in to 250 years before renaissance.
Define "Renaissance". Both of you, if you wouldn't mind.
so 250 years before renaissance... didn't they allready have primitive form of hot-air-balloon at that time?
I believe so. Heck, the Nazca had the ability to make hot-air balloons--there's just no proof they ever did.
wouldn't a magma powered blimp be so dwarfy... bridge is the best thing we have yet to make our dwarves fly.
Yes, but magma is sufficiently dense to overcome any lift it could provide. Especially since it shouldn't infinitely generate heat.
The whole elemental planes, I think, was kind of a very Dungeons and Dragons thing, I don't know if there was an earlier source than that, but ... so if that's not some kind of massive copyright infringement then that's a thing that people would like to have hanging around for whatever reason...
Good news! There's no way that WotC can copyright the concept of an alternate reality full of fire! (Christians would really hate that.)
I like a lot of those ideas for planes.
A few things I'd like to consider.
1. The general form of the land should be pretty much the same over all (or most) planes. Mountains are around here, mountains are around there. Ocean here, ocean there. Cold here, cold there. The exact shapes may differ--this peak here, that peak a bit to the south, the coast shaped a bit differently--which could be, shall we say,
interesting. Most plane-hopping things, or all but the strongest, or something like that should simply move you to the equivalent point on the other plane, or maybe a "safe" point nearby. Depending on the exact location, this could lead to hopping into a wall of solid rock (ow), falling a few z-levels, or something.
A couple of exceptions would exist. Some could have general, wide-sweeping changes, like a much higher sea level or lower levels of moisture overall. Artificial planes (e.g, Narnia-esque ones) could be a lot different, albeit much smaller. And, finally, some small fraction would be
different.
2. Planes should not usually be absurdly different from the "real world"--herein referred to as the "material plane". At most, two or three quirks. Maybe the Ethereal Plane is always shrouded in mist, has few mountains or hills, and is devoid of life. Maybe the Dreamworld gives everyone in it limited magical powers and is mildly sentient. Stuff like that. The thing is, these aren't whole different worlds so much as different aspects of a greater thing. Think about the word--
plane. Imagine old, 2DF. Now imagine a slightly different fortress above it--one where the Fortress Defense mod or something was applied. Above that is one where the dwarves live in an ehtereal-ish world, and past that is another normal-ish fort on a slightly different fort. And so on and so forth--you'll eventually build up a prism of worlds. The little slices, the worlds, are planes in the mathematical and magical sense...and no two next to each other are all that different. A bit of a simplification, but that's the idea.
3. Other worlds should mostly be inhabited. Not all the inhabitants will be familiar; maybe the Plane of Shadow just has darkness-adapted dwarves living alongside tower-cap-worshiping elves, but the Plane of Spirits would have much...stranger life.
4. As hinted at, no (or almost no) rules should be perfectly, always, perfectly, true. These are whole different universes, here. The concept of absolute laws is almost anathema to the entire concept!
4a. Each world's sentient modifications are pretty well separate from all this. Material Dwarves build a might Mountainhome in one mountain, but Shadow Dwarves might not build anything more than little outposts in that whole range. This helps when Shadow Dwarves (or whatever) start interacting with the Material Plane.