On the train from Paddington to Bath, with a tomato sandwich and a chemical-smelling cup of tea, I flick through my guide book.

Ancient rain, it says, fell about 10,000 years ago, soaked through to the earth's core, where it was heated to boiling - and the Romans built baths around the point where it bubbled, magically, to the surface.

Ancient rain, earth's core, Aquae Sulis - clean-jawed Romans in togas and, several layers of history later, sneery Georgians with their pots of slave-trade money and rich brocades and crumbling facades and wretched little black boy servants.

The day's dark grey and tinged with wet but, as the train slows through the shadowy, greenish-mauve hills and slopes which are the beginning of the city, the sun comes out with a big, yellow flourish and there's a collective, grateful "Ah!" in the carriage.

The woman opposite me puts down her magazine, packs her empty styrofoam cups and plastic milk containers and sandwich wrappers back into the Great Western Railways carrier bag. The sandwich pack won't fold and keeps springing back. I stare out of the window at the houses stacked above one another in eager, watchful rows.

Bath Spa Station it built of the same clean and hopeful blond stone as the rest of the city. A tail of skirts snakes onto the platform, queuing for the Ladies. Someone laughs. The air smells of sulphur and ginger biscuits - and rain.

I walk into the city.

I was a waitress here for two or three years. Every week I escaped the aimlessness of student life in Bristol to enter a world of working people and fat credit cards - Muscadet and Sancerre, hors d'oeuvres and gratin dauphinois.

The Saturday-night shift ended late and I always stayed over, allowed to share a room in the half-empty Georgian flat above the restaurant with my friend Dora, the assistant cook.

At five in the afternoon, in the dead time between shifts, Dora and I lay on our twin beds and talked about how one day we'd travel and have babies at the same time - at least a couple each - feeding them as we crossed borders, rumbled through mountains, wore flowered Oxfam dresses and ate Lindt chocolate bars and panini on foreign station platforms.

Dora played Peter Gabriel's "Solsbury Hill" several times a day and sang along and we smoothed Body Shop carrot moisturiser on our faces and I wrote poetry and Dora sketched. At six, I'd drag myself up off the bed and plug in the iron. My uniform was a Liberty lawn skirt with rust-coloured flowers. Spots and splashes of food hissed under the hot metal: steamed garlic, alcohol, fat.

Sometimes I stayed in Bath all Sunday with Dora (who was more dissatisfied and therefore more real to me than most of my university friends) and we wandered the city in a daze of tiredness, or else had a picnic with leftovers given us from the restaurant (though we were always on a diet) in Royal Park.

Now I walk down Manvers Street towards Westgate and the Abbey, past Sally Lunn's Tea Shop, the National Trust shop, the toffee shop, the baths themselves. Bunches of tourists and old people organise themselves quietly on the clean pavements. A woman is winding an old barrel organ against which a sign is propped: "Busking for the Mentally Handicapped".

In the Pump Room, aged 13, I learned to swallow aspirins for the first time ("Put the pill on the back of your tongue," said my stepfather, who sometimes wore a bowler hat when he visited historical places, "Then fill your whole mouth with water and swallow the lot.")

Five or six years later - before the restaurant job - I stood outside that same Pump Room kissing a boy who was serious and clever and slightly spotty and wearing a big army overcoat, which made the kiss feel like a Russian literary kiss. I was Anna to his Vronsky, though different universities - not other spouses - kept us apart.

Bath was the meeting point. We were in love but even then we knew we brought out the worst in each other. He told me I was frivolous and that he couldn't concentrate on his work when I was around but, standing at dusk in the Garden for the Blind in Henrietta Park, he remarked with a pained expression on his face that he was going to marry me one day all the same. It wasn't a proposal or even a question (more a Lawrentian sacrifice on his part), but it seemed electrically romantic to me at the time and it meant that for years I was able to half-lie to people (and myself) that I'd been proposed to. Once.

Now (an edgy 35 and with three babies and not a lot more travel under my belt), I walk in the deserted Garden for the Blind in the acidic April afternoon light. Not a Russian overcoat in sight. The plants are named in Braille and in summer the smells are precise and pungent. I sit on a bench and close my eyes and think about what it was to be 18 and frivolous and mostly alone.

Dora had three babies, too, and lives in the country and runs her own catering business.

When I open my eyes again, there's a man with a briefcase walking purposefully to the Gents public toilet. The flowerbeds are recently hoed, the soil piled dark and sticky. My life is rich; these days, I have to grab, conjure and imagine loneliness.

A blackbird sings, shrill and disjointed. The last dregs of sun are squeezed from the sky.