'My first story was, in a way, an affectionate pat on the back for theUnderground, a love poem for a creature that is underrated

The first time I travelled to London, 20 years ago, I fell in love with the Underground - in fact, with all things subterranean and hidden.

Over the years, I've amassed a fair collection of books on such subjects as Tube architecture, "dead" stations, Brunel's tunnel, the Post Office's 23 miles of track, the 8,000 miles of gas and water pipes, Bazalgette's sewer system, war bunkers, the Channel Tunnel and, of course, London's lost rivers. But that first Tube ride had an impact I've never forgotten.

To be part of a vast, captive tribe, with all the tension and nervy territoriality that entails, is infuriating and exhilarating at the same time.

And the whole Underground matrix has a pull for me that operates on several levels: as a practical miracle of modern engineering, as a collective endeavour in some grand social experiment, as a combination of the aesthetic and the mechanical, as a metaphor for 21st-century anomie, as the repository for a million human stories: in all of these arenas, the Underground is impossibly and matchlessly romantic.

When I sat down to write my first short story, I hadn't lived in London for years, but the Underground was the first subject that swam irresistibly into my head. I remembered my first journey and the people beside me, opposite me and all around me, each one potentially more fascinating than the last.

The result was Sub-Aqua, which combined the tale of a traumatised Tube driver with a woman's quest to track down those lost rivers: the Neckinger, the Langbourne, the Fleet, the Falcon, the Effra, the Tyburn.

I was sufficiently satisfied with that story to decide I might as well write a second. And then a third, and so on, until, all of a sudden, I had a collection.

I'm still obsessed with worlds of concealed and benign subterfuge, those layers of life that exist beneath every great city and without which they would grind, groaning, to a halt.

My first story was, in a way, an affectionate pat on the back for the Underground, a love poem for a creature that is underrated, overworked, ageing, crumbling, criticised and unloved.

I look forward to the underground section of Luas, in Dublin, with keen interest.

• Big Mouth, by Blánaid McKinney, is published by Orion, £6.99 in UK; The Ledge, her first novel, is due out next month.