We met Alex and Aethan in Vauxhall by the MI6 Headquarters. A discussion of the unknown, but highly probable possibility, that its pyramid-like façade was merely the tip of the iceberg for a vast subterranean complex set the mood for imagining what else might be concealed beneath the viewable landscape – and indeed how the make-up of the physical landscape has been affected over the years by these invisible structures.

The muddy shoreline where we gathered, provided (as well as an opportunity for some mudlarking) a view across the Thames to the mouth of the River Tyburn – the now almost invisible landmark that we would attempt to retrace and imagine throughout our walk.

From this vantage point, Alex and Aethan pointed out the bronze statues that adorn both sides of Vauxhall Bridge, which are only viewable from the river. Alex and Aethan informed us that one side of the bridge represents the humanities, and the other, the sciences.

Retracing the river, it became apparent how the surrounding built environment had grown up around it, and as the city had grown, and space became more and more of a commodity, the river was covered over. The Tyburn, we heard, is just one of many of tributaries that run through London – most of which are culverted – whether for convenience or sanitary purposes. This was most apparent on Tachbrook Street, which follows the course of the river itself and evidently bows in the middle. On either side of the road, two distinct architectures – both in style and age – face each other. The river was audible through a drain in the middle of the road.

-Tom Spooner