I'm looking for a blog post I saw on HN some years ago (maybe 3) about an underground electricity sub-station. It may be been couched as "what's that mysterious building" or somesuch, but it delved into high-voltage cables and how they need to be cooled with (flammable!) cooling oil. It was fascinating, and I'm keen to re-read it, but Google fails me. Hoping the poster is still around... and sees this before this question (rightly) gets taken down :-)