The Strategic Petroleum Reserve→

BBC:

But there’s not much to see above ground – merely some wellbore heads and pipelines. The wellbores themselves plunge thousands of feet into the caverns below and can push water in at high pressure in order to retrieve the oil through a process of displacement. Corbin adds that managing such infrastructure comes with unique challenges. The salt caverns are not completely stable, for example. Sometimes bits of the walls or ceilings may crumble away, causing damage to machinery which has to be carefully replaced. It’s not possible for workers to enter the caverns physically so, like drilling oil out of a natural well, it has to be done remotely.

Am I the only one that finds these big, not-secret but just not-well-known infrastructure projects fascinating?