Oil
I'm doing some work for a client in the oil industry (before my environmentalist friends start attacking me, the project I'm working on concerns what this particular company is doing to cut down its contributions to greenhouse gas emissions - and the answer is "more than I expected, actually").
Part of my research has led me to this website: Offshore technology. Browsing through the descriptions of all the different projects makes fascinating reading for anyone with even the slightest mechanical inclination - there are some impressive feats of engineering being described here.
As someone who grew up on the east coast of Scotland, I had several school friends whose fathers or elder brothers worked "on the rigs" and, while my hometown of Dundee is not quite on a par with Aberdeen, Britain's oil capital, I do remember seeing oil rigs being built in the River Tay when I was a boy.
I also remember Piper Alpha, a reminder that those who drill for oil are quite literally playing with fire.