IT is good to be alone with a cathedral. Especially this one.Strasbourg's cathedral is a miracle of lightness. Its massive spire - for 400 years the tallest in Christendom - seems to lift the huge structure off the cobbled surface of the old city square. "It's lace in rock," a resident says. Even the rock breathes poetry. It is gres rose des Vosges, or red sandstone from the Vosges. Its rich color is startling in any light, but in the last hours of day, the walls shimmer ocher red. This is the best time to find a cathedral alone. The tourists who streamed in at 12 sharp to see the stained glass in its noontime splendor or the 60-foot, 16th-century astronomical clock run through its paces have gone: The 12 Apostles and four ages of man have turned solemnly past, the golden cock has flapped and crowed, and cameras have been tucked away. In the quiet of a late afternoon, the nave of the cathedral is shadowy and hushed. Yet even in near darkness, ribs and vaults, towering jeweled windows combine to give a sense of motion, lightness, and light. High Gothic sculptures brighten corners, and stone figures seem to walk out of pillars. Their tender faces and deeply creased robes appear captured in an instant of thought and movement, as if cast in liquid stone. End of day is also the best time to find local cathedral-lovers with stories to tell. The Gothic masterworks are in guide books, but had I noticed the little dog sleeping at the base of the carved stone pulpit? asks a kind, self-appointed guide. There was a clergyman who preached long, earnest sermons - so long that his pet dog, who accompanied him everywhere, would fall asleep. Here, right here, is that dog, still sleeping. This cathedral has a sense of humor. And had I heard that the stained-glass windows had been removed during World War II and hidden in a salt mine, discovered by American soldiers at the end of the war, and restored piece-by-piece, and not one broken? Several of the soldiers who found the glass returned to see the cathedral last year, my guide says. Perhaps that's part of the reason there were street protests in Strasbourg to keep the American consulate when Washington proposed closing it, my guide adds. Could I think of many other examples in the world of street protests to keep an American consulate? The cathedral laughs, again. Time has been less kind to the walls of the cathedral. The sulphur released into the air by fossil fuels as the Rhine valley industrialized has had as devastating an impact on the cathedral as on the trees in the Black Forest on the other side of the river. Scaffolding is a permanent feature of the cathedral's outer walls, as a full-time battle of restoration is waged against the corrosion of smoke and gasoline fumes on sandstone. These outer walls provide another way to be alone with a cathedral: Walk up the narrow outside steps, past omnipresent scaffolding. Stop to look out upon piggy gargoyles or the flying buttresses that made all this Gothic lightness and verticality possible. From the landing, look down the line of angels' trumpets, down to the square that marked the center and high point of the old city, and over to the distant Vosges mountains, with their rich vineyards and abandoned textile mills. Below, where medieval tradesmen once mingled, Senegalese vendors hawk leather belts and hats, shop owners display postcards, Alsatian dolls, and cathedral kitsch, and students gather late into the night to talk. Photographers strain to find some way to fit the whole cathedral into their viewfinders. That is difficult. While the cathedral is unmistakable from a distance, it is lost amid the narrow streets and gabled half-timbered houses of the old city. But not lost to those who alter their courses just a block or two to watch the light pass across the cathedral's face. In this city of walkers, all roads lead past the cathedral. Claude Monet painted the cathedral at Rouen 30 times. These walkers know why.