There’s a stalactite in the Undercroft, the skatepark that hovers beneath the Southbank Centre. It has a stalagmite growing beneath it, both are lumpen and ugly with the awkwardness of youth. They are yellowish, constructed by the fervent dripping of a leaking pipe. I’d already clocked it when M points it out, this strange mineral growth in a fortress of concrete and lurid spray paint. We walk down the steps and wonder about this bunker’s origins. Was it made with this intention, built to contain the clank of wood on concrete and to have its grey edges coloured in over and over again, or did it emerge like the stalagmite, uninvited and persistent?

The skate park beneath South Bank Centre is its own kind of pothole, extending far further than you can see from the metal bars separating its edges from the pavement, from skater and audience. I’ve stood there often since my teens, looking on. These days I’ll dismiss the Southbank as touristy, but the fact is I’m drawn there more often than I care to admit. 

Once again, we’re walking along the river. This time we have it all to ourselves. It is dawn, though the sunrise hides behind the clouds. The grey light is appropriate for this time of day, really: too late to be night, too early to be morning. We are caught in-between, a kind of nowhere place of our own.

If we are starting our day - we tried to see a play where a woman did the same scene over and over for 24 hours, but the queue was too long - the only other people we see have been leftover by the night. Three French men balling their way towards Blackfriars Bridge, who shout enthusiastically at the baby strapped to my chest. Four people in their twenties on the banks of the river about to be caught out by the tide. One of them has not covered her waist, a soft curve against the murky sand, and I feel a chill and my age at the same time. Two girls in their early twenties who were giddy on fatigue and wine and friendship, sparkly eyed and scruffy-shoed. They had been to a Cabaret in a working men’s club out East and hadn’t got home yet. I wondered if they would bundle into their own beds or share one, in the way girls do when they are young and heating is rare and expensive. Perhaps they also feel they have, for one slippery moment, seized hold of London, dived into a secret place where people should be but aren’t.

By the time we reach Royal Festival Hall we have passed them and bankside stretches out empty. We walk around the Undercroft and it feels somehow illicit to enter this place so hallowed by four wheels and an entire subculture. I remember writing about it a decade ago, when it was threatened with closure, when there was a chance it would become a line of coffee shops like so much else of the city. The skaters won out in the end.

Out onto the pavement and between the pollarded plane trees. Across the river there are still cars on the Embankment but so few that we can hear them distinctly whoosh by, rather than the city’s constant hum. I think of how we drove down there on our wedding day in a black cab, how the light splintered off the water.

The Thames washes in, the tide rises, and I let out a cry into the air. London feels new again this morning, even among all our ghostly younger selves, even as the fog wraps around its towers and the tang of the ancient water wafts up. How odd and alive to be awake now and not in our house. I have seen this hour most days since C was born, but always in the same two rooms. All this time the city was waiting for us.