I got 2 blueprints I only don't know how I got them. I know how I can use them, for different building.
My guess is that I get them from sending Hunters.
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Sign up to join this communityBlueprints can be crafted at the Workshop once you have the right technologies, but they cost a lot of science and culture to make (indirectly, through their requirements).
The other way to get blueprints, which probably happened to you, is through trading; every trade has a 10% chance to give a single blueprint.