Last Sunday, amid crisscrossing travellers scanning the noticeboards, some enthusiasts were dancing the Argentine tango. They had rigged up a sound system and, punctuated with crackly announcements of trains departing for Zaragoza or Santander, the sleazy, soupy wail of the accordion-like bandoneon floated down the concourse.
The surprising thing was not so much the unlikely venue. A station is actually very appropriate for a dance - or, for true fanatics, a philosophy - that is all about restless journeying, longing to return, and wishing you had never gone away. And there's even a bar on hand.
What surprised me was the enthusiasm, the joy and warmth on people's faces as they clung to their partners or watched shyly from the sidelines, minding their bags.
Despite the obvious Latin link, the tango has aroused less passion in Spain than in Germany, Britain or even Finland. I think Spaniards are just not gloomy enough. Tango is about decadence and loss, nostalgia for past happiness, a dance of passion and despair invented by poor immigrants to help them forget a harsh present and a hopeless future. But these couples, some old, some young, were having a whale of a time executing those complicated steps and swivels.
One guy had it to perfection. Thick black hair slicked with "gomina", patent leather shoes, and an expression of grave concentration. Tango etiquette is clear: a woman must never invite a man to dance, and a man will never ask a woman until he's seen her dance. The usual way round this catch-22 is to enlist the help of a male acquaintance to "varear" - a coarse gaucho word for trotting out a horse before potential buyers.
So I was breaking two taboos when I touched this man on the sleeve as he leaned against the station cafe with a cigarette between his fingers. "Can you tango?" he asked doubtfully and, just to make sure, led me a few turns behind the Coca-Cola vending machine before committing himself to the full public glare of the impromptu dancefloor.
He was Chilean. "I came to Spain a year ago because I don't like the social situation in my country. I thought this would be a happier place, and it is." And how did he find the tango scene in Madrid? "Fantastic. Most tango dancers who come from South America are couples. I'm single so I get lots of partners."
After a while, the couples thinned out, people picked up their bags and headed for trains and taxis to take them somewhere else.
TWO BIG department stores face each other across the busy intersection near where I live in the heart of town, where the pavements are always crammed with surging crowds. That's no deterrent, rather an encouragement, for a trumpeter who instals himself with this back to the road and contributes to the hubbub by belting out stirring paso dobles. His female sidekick commandeers the other side of the pavement and weaves obstructively amid the human tide until money is extracted.
The trumpeter had an impressive keyboard and amplifier system banked up around him, and closer inspection revealed this to be the source not only of the thumping electronic rhythm accompaniment, but the brassy trumpet melody as well. We were being asked to donate to a tape.
MADRID'S TUBE trains draw two main sorts of musicians: gypsies with tattered accordions and their chant of being unemployed with five children - a plainsong often more tuneful than the ragged jig that follows.
Then there are youngsters from those Andean countries that produce panpipes and brightly woven shoulder bags. A cheerful greeting, a burst of "El Condor Pasa" or similar, a trot around with shoulder bag extended, then they bundle out at the next stop. People usually give 25 pesetas, about 10p.
But now and then a gaunt bluesman lurches aboard. No spiel, just haunting guitar and harmonica.
The other day he played the Eagles' lament "Hotel California" as if his heart would break. His eyes half-closed, his face grey and impassive, he faltered down the carriage like a forgotten Yardbird, the only one from that triumphal Sixties season at Richmond Station Hotel never to star in a mightier band.
He dipped his guitar before each passenger, and I was not the only one to trickle a torrent of lentil-like small change into a cigarette packet stuck behind the neck. He tweaked a schoolgirl memory and a pang of nostalgia that any tango fan would relish.