Arcane Technology:
Our greatest scientists have been looking at the notes of the vault. Some of them were initially dismissed as the ravings of a madman, but as we begin our ascent through the tower, they’ve been looked at again. Every advantage is needed, after all; if it could lead to some small advance, why should we not commit the resources to learn? So our scientists look through the notes. Some tell of things that are in fact what we think they are, basic physics and such… others, not so much. At the direction of their bosses they decided to experiment with the nonsensical ideas anyway. One was something about spirits, which after seeing the formula the scientists naturally took to mean a form of intoxicating beverage. They proceeded to take the "recipe" and make a brew - and quickly learned that it wasn't exactly the kind of spirits they thought.
The physical world is not the only one. There is a second one, not in another location, but the same… just sort of, beside our own. The scientists took their drinks, and after savoring the shockingly good taste, could suddenly see wondrous things in the spires of the fortress city, things nobody else could. If it had been one, we could suspect that someone went mad from the experiment. But all of them reported the same. Pursuing the notes further, now with a serious eye, our scientists have learned how to change this from simple knowledge for the sake of knowledge into practical gain.
The other world is described by the notes as a world of spirits. There are human spirits, but just as if not more common are natural spirits, spirits who embody concepts and elements - we’ve seen spirits of joy and anger, of water and light, and more. All very interesting, but how can we use it? Well, we’ve also discovered, in the notes, a means of drawing in and containing spirits who can provide wondrous properties to whatever tech we happen to put them in. Using artificial crystals that attract spirits, the type dependent on the formation of the crystal, we can use their powers in our technology.
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Before we can begin to use these astounding finds for our equipment, we must first make the crystals. The few we painstakingly crafted for testing will not last long as we build up to war. Thus, our first step is not to make gear, but to create an industrial scale process for creating them. We've dubbed them spirit crystals, which if a tad unimaginative is at least descriptive. We've sectioned off an area for the production facility, contracting dozens of our citizens to swell the ranks of the "arcanists" who specialize in dealing with the spirit world. The laboratories are filled with machines taking the various chemical and metallic ingredients, and forcing them into crystalline form. The arcanists then proceed to inscribe the proper runes on them, and then trap the spirits inside. Then, they go and do it again, and again, producing the crystals to fuel our creations at an industrial speed.