Anyone recognise this mains power connector?

Industrial power connection, multi-pole. Still used today. Here is the modern day equivalent.

Thanks Ross. I suspected it was something like that, although I was hoping it might be something more exciting. :)

One thing I found interesting is that the wall wiring appears to be encapsulated in brass(?) tubing. Before I peeked inside I thought it was some sort of air outlet.

I suspect the cable sheath is copper. Fireproof cables are commonly used for fire protection systems and where industrial machinery is connected. The most common brand of cable I know of for this application is Pyrotenax.

It looks like a flameproof fitting for use in flameable situations like areas with solvents or other dangerous situations

Or explosives, in this case... :)

It's used wherever it gets hot. We use it on the boilers in a poer station, but it's also used where it's important to have equipment running in the event of a fire, such as a water pump. Also used on ships and emergency equipment or where you need to run a big current through a small cable.