I went to buy some new trainers the other day, and did, in fact [or in actual fact: I didn't], and wearing these trainers I walked over the anti-slip pattern by the traffic-lights crossing Oxford Street from the north to south -- and actually I can't remember exactly where it was, possibly near where C&A used to be, but that's not important, what is, is this: the combination of the bumps of the anti-slip overlaid (underlaid!) on the modern pseudo-random bumps that are the tread of my shoes spelt out a message in braille on the bottom of my feet: the message directed me to such-and-such portion of the night sky at such-and-such a time and date, with blah magnification.

And so you know what, I did that, thanks to my new handheld GPS and some free binoculars I picked up at a server farm launch party at the tail end of the dot-com goldrush, and there was another message, also in braille: The Lord's Prayer, written nearby M31, in nebula and stars and the glints of satellites, and actually for one point, the taillight of a 'plane. You won't be able to see it now, a miracle!

Actually, that reminds me of another story, of before Transport for London when the tubes lived underground like moles, before we sunk the escalators and elevator-terriers, when the tracks were fresh, and the trains ran on time, and they painted beautiful mandelbrots with chalk and clay, and made love in the dark, and if you stood under where Centre Point is now - in that hub that we're digging up and trashing - and faced east, you could feel the sea air on your face, the wind from Southend-on-Sea.

The trains used to call to one another down the foot tunnels, their clacking voices whispering poetry as they passed, seducing, romancing in the 30 seconds before their doors would have to close, sometimes dwelling for up to a minute and - if they were lucky - a signal would get stuck on red and they would enjoy sometimes a quarter of an hour more in muttered sweet nothings, voices zigzagging down the corridors like light down fibre optics, or transmitted in the changing arrangement of the wall-tiles, every second more beautiful than the last thanks to the growing intimacy, but more painful because the end must be getting closer.

At Green Park once, long before it was called Green Park, the love to end all loves came to be between a train on the Piccadilly Line and a train on Jubilee. This was in the middle of an age of irony, and shone like a diamond, even brighter for being surrounded by aging tracks and scuffed seats. A chance broken rail meant these two lovers were granted hours together, and as they finally broke through the lack of earnestness that characterised those years, opened up to one another, they admitted with full frankness and not caring whether it was reciprocated, because this was so true, the truest most pure thing there had ever been, etc, they sung down the foot tunnel, simultaneously

I love you

and these two messages met in the middle of the tunnel-conduit and set up a standing wave, and in a catastrophe this wave crystallised and became fixed, lodged in the walls, and whereas before the decoration of the walkways acted as a substrate for encoded signals to zoom along at a much greater group velocity, these messages become solid, like concrete: and this fixedness spread through the tunnels and the trains and the tracks and the interconnects and the ticket barriers like a virus, and it killed them all.

So that's where we find ourselves now, travelling in the fossil shells of an ancient civilisation, trotting down lava tunnels where the lava has gone, and that's why when we tapped our first boreholes down through London we didn't hear singing.

But if you walk at Green Park down that walkway, between the Jubilee and Piccadilly lines, look at the intricate tile pattern on the wall, blues and whites and turquoise, and know what it really says, in the language of the London Underground.

And, as it happens, if you decode it into ASCII instead, into English, the tunnel walls spell out the whole of Beowulf too. But that's just coincidence. It doesn't mean anything.