World's submarine wiring:
Considering that, they are essentially, part of the same machine, these would actually be the largest human infrastructure projects in existence rather than bridges & tunnels.
They might not be visible from space, but they are planetary sized.
I have seen somewhere the proposal, of building a cable ring around the earth (a coil). By rotating through the Earth's magnetic field (or the Earth rotating through it), it would act as a big generator. Electricity then would be beamed down to the surface. I don't know if this would work, but it actually sounds easier to do that space solar panel and stuff and I am a bit annoyed that I can't find that text again.
