The Westbourne is the third of seven underground rivers in London whose above-ground course we have been following on annual excursions.

The source of the Westbourne took us back to the source of the Fleet, as explored in 2013: a dew pond in Hampstead Heath which also represents London’s highest point. This time I took the trouble to look up what a dew pond was rather than merely thinking ‘hm, dew!’ and leaving it at that. The lost rivers walks are intended to instil a sense of curiosity about the environment in the walkers…. by this point it’s working! (a dew pond is an artificial depression at the top of a hill made to collect ‘dew’ or more likely, rainwater).

Each river’s character is subtly different. The Westbourne proved to be the most elusive so far – we didn’t see it from ground level at any point, while the Fleet and the Neckinger occasionally revealed themselves. The dew pond apparently doesn’t count, and at this early stage all we had to go on was the shape of a valley and some reeds at the foot of a dip in the land revealing a watery presence. Residential gardens are described as being mossy and clayy, the book’s author pointing a finger at the river for this.

I like the experience of getting to know Tom’s character through these annual excursions. The walks we undertake are at once Tom’s published river walk, witnessing the changing nature of the landscape even since 2011, speculation about the publisher’s requirements for the book’s content, and seeing what is left out as much as what is included in the text. My favourite aspect of the walks is our group’s own responses and discoveries – my take is that this is why we are here. An early moment is spotting the name ‘Welbeck’ on a building: it’s clue for our greater consideration, rather than evidence of someone responding to the river’s existence. A watery term emerges a few hundred yards later: ‘Solent’ Way. The Solent is a strait rather than a river and its appearance may well be accidental. But it’s the moment of feeling that you may be reading / decoding someone’s hidden intentions that is the thrill of London’s Lost Rivers.

One such moment occurs at a right turn into an alley: decorative arches in a wall mark the presence of the underground river – ‘either by intention or accident’. The phrase splits the whole project apart: what are we actually doing here? As the ‘guide’ I’m happy to look for material myself and weigh up what it might mean, using the book as a prompt rather than a comprehensive authority. I’m happy for Tom Bolton to share his observations too rather than announce he is a river authority. I seemingly inconsequential feature such as these brick arches would be nearly impossible to trace or research the real intention of. Would we want that info to be included anyway? Certainly the publisher wouldn’t. It’s worth mentioning at this point that I skip most of Tom’s interstitial theatre history / crime site inclusions in the book – we’re really just here for the river. Occasionally I feed one to the group when there’s more than a quarter mile between grids in the pavement or effluvial valley evidence in the street layout.

Something else became apparent this year too, a clearer understanding of the purpose of the walks and how they sit within the wider practice of guided tours. I’d recognised that by dropping sight-seeing as an intention for looking at our surroundings, it allowed the group to focus on the ‘invisible’ aspects of our world. This could include the shape of geographical landscape, or shop, place and street names, drains and manhole covers and more. The format of Lost Rivers allows something else interesting to happen: essentially I’m acting as a very sketchy guide for the event by doing no preparation at all beyond bringing Tom Bolton’s guide book London’s Lost Rivers. I’m at once tracing the route, skimming the text for river related information and only occasionally looking up for evidence of the river’s presence – at this point I usually take the group the wrong way and miss key bits of the rout as it appears in print. The task of observer falls to the group. We suspect that Tom leaves some aspects of the river to be discovered by the dedicated walker – a reward for exploring from beyond their armchair. In the absence of a reliable guide, i.e. me, the group are encouraged to (and basically need to) sharpen their observational and interpretative skills to benefit from the walk. In some contexts this would be unacceptable behaviour from the guide but in this context it worked quite well. I’m merely inviting people to come with me as I negotiate the book and the unfamiliar city and I enjoy the feeling of being a group member of my own tour. That said, I think next year I’ll at least become familiar with the route we are supposed to take: this time absence of street name markers was incredibly frustrating.

At one point, I get the map wrong and lead the group along a street-too-far. It reveals the crazy PoMo architecture of Netherwood Day Centre but also means we come across some run-off water flowing across the pavement from a down hill section of the local landscape. Should we call this the Westbourne (or the Kilburn, as the river occasionally changes its name)? All rivers are essentially run off. We’d earlier consider the scale at which a stream became a river (there was no obvious answer).

There are two moments that haven’t appeared previously with our river pursuits. The first is outside a disused pub called the Bird in the Hand our attention is drawn to a battered hatch in the pavement, since replaced by a new cover. An enterprising member of out group recruits a nearby washing machine delivery man to loan him a screwdriver to open the hatch. With a group lifting effort, it’s surprisingly easy work. A brick lined shaft to a lower level is revealed along with a vertical metal ladder and an overwhelming pong of sewer. None of the group is brave (or stupid) enough to descent the 20 feet or so to the river’s edge, although it is clearly audible from street level. While we’ve encountered these access points before, this is the first time we’ve actually opened one up.

The second new encounter is the treatment of the Westbourne as it passes an unavoidable underground space: the District Line as it arrives at Sloan Square. Here, just above platform level, the river is channeled through a four foot diameter iron pipe. It is not obvious without the guide but we are at our nearest yet to this mysterious river. At an earlier juncture, we stop at Hyde Park for ice creams. Behind us is the Serpentine pond – seemingly an extension of the Westbourne. Indeed we look for the grate through which the Westbourne flows into the pool (as with the Fleet). There is none, as the river bypasses the pool. Underground pipes quarantine the stinky flow hygienically and aesthetically through the park.

Another phenomenon is the discovery nature of the changing city, more obvious with each annual excursion. Some of the back roads travelled by Bolton mean that it can be hard to use a handy landmark to show you are indeed on the right track. Grassy banks are mown and a car park barrier described as being red and white in 2011 has since had a slick, black makeover. A distinctive tiled pub included as a bonus feature of the river walk has been since been smashed (illegally) by a property developer. How might this travelogue read in 2051?

By the end, we are exhausted, blistered and walking for the sake of completion. I am reprimanded as to what I left out of the crime / dark local history sites: Judy Garland’s deathbed location is missed especially. Various blisters and sore feet are nursed – this was a longer walk than we expected. We also somehow miss the river flowing into the Thames – the only glimpse we would have caught of the water itself. Somehow this feels the correct outcome for the most illusive lost river yet.