Lilian Pizzichini basks in the sandstone glow of the ancient city of Salamanca
It is easy to make a case for the ancient university city of Salamanca being the loveliest and most graceful in Spain. Once I was within its walls, which insulate it from the rest of Castilla y Leon, and I became immersed in its antiquity and culture, the contemporary realities of Spanish life simply faded from view.

A stout Roman bridge straddles the calm waters of the river Tormes, and I paused in the middle to watch Salamanca rise sedately on a hill weighted with venerable buildings leading towards the pinnacle of the magnificently theatrical Plaza Mayor. As I walked along the gently listing, cobbled streets, El Greco faces peered at me from the windows of bars when they weren't elegantly sipping from a glass of fino.

The pace is gentle in the sleepy little squares that radiate outwards from the main drag. I sat at one bar for an entire afternoon, taking in the warm, reddish gold light that refracts from the walls of the sandstone churches. A vivid pink Campari goes very well, I thought.

But back to business. Salamanca's two great cathedrals - one Gothic, the other Romanesque - are linked by a stone wall. The "Old Cathedral" dates from 1160 and announces itself with a silvery, scaled Byzantine dome, flanked by turrets and presided over by a golden rooster. The frothily exuberant "New Cathedral" was built in 1560 as a celebration, not of God, but of the University's worldwide eminence. The edifice is a complex mass of carved images, the interior exotically Moorish, done up with gold leaf.

Salamanca's other famous landmark is the eccentric, 15th-century House of Shells, embellished with sculpted conches. But, full of Campari and eager to escape the searing heat, I found my resting-place in the cloistered, magic garden of the 16th-century St Esteban. Its facade depicts his martyrdom (death by stoning) in glowing terracotta pink, the pillars of its cloister snake downwards in sensual curves.

After a day or two in this aesthetically soothing setting, you cannot help feeling it was the city's architects' intention to construct the perfect ambience for a sleepily studious existence. Fittingly, it is Salamanca's 13th-century university, which after Bologna and Oxford is the oldest in the world, that is considered the greatest architectural expression of the Spanish renaissance.

The university was constructed during Charles V's reign. The stone arches, wooden ceiling and tapestries of its paraninfo, or main hall, are uncommonly grand. The students' wooden desks survive from Charles's day, as does their graffiti. The paraninfo is legendary, as is the city, for being at the epicentre of Spain's radical intelligentsia. Its most famous lecturer was Fray Luis de Len, a mystic preacher and poet who was taken from his pulpit for questioning by the Inquisition. When he returned, five years later, he opened his lecture with the words: "As we were saying yesterday...".

The stone stairway that leads from the hall to the cloister above is decorated with grotesque reliefs. Beyond this is the library where the monastic hush is impressive (they take their learning seriously here). An upwards glance reveals the dizzying plateresque carvings on the ceiling. Salamanca is home to the plateresco style, and it is more baroque than the most frenzied of Italianate excesses. Once outside, it is essential to study the facade to find the "Salamantine" frog perched on a skull - a reminder to students of their mortality.

On to the more cheerful, 18th-century Plaza Mayor, where farmers still conduct their business. The square is literally the city's heart of gold, designed by Alberto Churriguera, the father of plateresque finery. It is constructed from piedra de Villamayor - a sandstone that is pale and moist when first quarried, but after years in the sun hardens and darkens to a deep, golden-brown. It is a glorious stage on which the Salamancans display themselves, criss-crossing the enormous paved square to meet friends in one of the bars that ring it, or where they flop on to its stone benches for a snooze.

Above the porticoes rise majestic, three-floor mansions with iron balustrades. Old ladies sit on their balconies to watch the town at play beneath them. Children play football, students flirt, and grizzled old men complain about it all. By now, of course, they are all indifferent to this breathtaking monument to stylistic unity. But for the visitor, its majesty takes some time to absorb.

As dusk falls, the light changes dramatically - from vermilion to rose to pale amber. This is when the Salamancans get romantic; guitars are brought out, raucous singing begins; babies dangle on laps while their mothers nibble at roast suckling pig (Salamanca's favourite dish). The square at night, in contrast to its daytime listlessness, is turned into a riot.