Self-constructing

As we all watched with a mixture of terror, awe and confusion, the orphanage slowly began building an identical structure immediately next to itself. I didn’t understand what it was doing until several hours in.
Vertical beams first, with inner and outer rings where each floor would eventually be. Then plumbing, then electrics, including the dynamo. Some mechanism manufactured for the purpose was placed in the center and, once steam built up, it began to burrow into the Earth.
In search of metals, no doubt. And to reach the water table, which the newly constructed second orphanage would draw on for steam, for drinking water and for coolant. Level by level the pivoting, articulated mechanical arms extending from the first orphanage assembled its twin.
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Self-assembling; Self-gathering