I used to be obsessed with subterranean worlds. Underground rivers, tube lines, tunnels (I still find strange comfort in tiled pipes full of people). At the time I now realised I was probably suffering from what is called Generation X Early Adopter Paternal Depression. Our daughter had been born a few months before the start of the new millennium and I’d ended one relationship, started another one and moved house in the months before she was conceived. For the first time in my life I began to feel that my normal bouts of melancholy were deeper than usual. This was a hard-to-shake melancholy. Rather than seeking any kind of support, or even talking to my partner about it, I embarked on what I saw as a redemptive quest to discover and walk the routes of long-buried rivers in the capital. It became an obsessive project. My feeling was that by tracing these lines I was acknowledging my own buried psychic discomfort, at the same time being open to the mind-altering powers of extra strong lager as a water divining tool.