According to the description, Thermal generators must be built "over steam vents". Naturally, I assumed that this meant the space above the one marked "steam", so I cleared out rubble and tried to build on that space, only to find that I could not.
Do I need to actually build on the space that says "Steam", or above it as the description says? If above it, is there any reason I can't build on a space I've cleared out? (other than money, which was not an issue).