[I]n a north London park, we crawled under fencing, pulled away a heavy iron lid to reveal a shaft in the grass, and descended a rusted black ladder into darkness.

Twenty feet down we flicked on our head-torches – and whistled at what we saw.  Dozens of brick archways extended in series away from us, the dips between them holding wide rungs of still water.  The iterated forms of the archways and the reflections of the water created the illusion of infinite regress.  The echoes of our whispers bounced back to us.  We had entered a mid nineteenth-century reservoir, built to serve as a water depot for London and now drained almost dry.  The once-drowned structures were still intact, the brick as clean as if it had been built yesterday.  It possessed the functional elegance of major Victorian infrastructure, and was as beautiful in its way as the Roman cisterns at Misenum and the Basilica Cistern in Istanbul.

We walked the reservoir end to end and side to side, our voices booming.  Above us in the shadows hung the ceiling vaults, made of tens of thousands of yellow-brown bricks.  At the far end of the reservoir we sat for a while.  Bradley smoked and set music going: a drum-and-bass track called ‘Stresstest’ that boomed off the bricks.  We got out just before midnight.  There were scattered clouds, underlit pink and orange by the city’s light, with stars visible between them.