There is little doubt: this church is one of the ten most important buildings of the 20th Century. There are taller buildings, bigger buildings, more expensive buildings, but I doubt if there is any building built during the second half of the second millennium AD that reflects the human spirit more perfectly.

In the great tradition of cathedral building, almost a century after the church was begun, it is not much more than half finished. This building will probably not be finished in our lifetimes, but even as it stands today, it is impressive beyond words. Visiting it, one walks through an active jobsite, with half the area fenced off and occupied by hard-hatted men and women busily a-building.

The great spires of Gaudí's unfinished church of Sagrada Familia are visible from all over Barcelona, reminding anyone who sees them of the aspirations of the human heart. As one draws closer, the decorations on the spires and facade make this reminder explicit: Hosanna in Excelsis, Sanctus, Sanctus.

A devout practicing mystic, Antonio Gaudí's vision for the church incorporated the whole sacred family, Jesus, Mary, the Gospelers, and the Apostles, each represented by a spire clustered together to form a great church.

The east facade, finished in Gaudí's lifetime (and therefore 75 years old) tells a hopeful story about Christ's birth as interpreted by an animist: Gaudí surrounds the legend with the realities of life in Catalunya, including goats, turtles, snakes, and farmers. Using varicolored stone, stained glass, and enamel mosaic, even in the shade this facade glows (but not especially well in photographs; sorry.)

It was mid-afternoon when we arrived, and the east facade was in shadow. Within, light shining through unglazed rose windows speckled the massive columns that grow like the trees that inspired them around the nave of the church. Hoping to catch as much light as possible, we walked through to the eastern portico, and looked up ... up ... up. Gaudí's spires serve as steeples and spires are meant to do, to draw our eyes, and thus our thoughts, heavenward.

We were eager to get up amongst the spires and see the decorations on the spire-tops, so we found the elevator -- cylindrical, as befits the round towers -- and up ... up ... up we went. At the lift's top, another set of stairs led us upwards to the high bridge between the two tallest eastern spires, unimaginably high up -- well, at least 100 meters...

Looking down, we are reminded that Sagrada Familia is to be a parish church, intended to serve a prosperous neighborhood near the center of the city. Below, the spires cast late-afternoon shadows on the neighborhood's apartment blocks. How late it was getting! How much more there was to see...

We started down the spiral staircase around the inside of a spire that looks small and delicate from outside, but feels rock-solid and thankfully earthbound from within.

From here, we could easily see the decoration on the spire-tips -- Hosanna in Excelsis. The spires are crowned with crosses encrusted with fruits, oranges, fanciful knobs, as one might expect of the author of Casa Milà. From here, it seems as if one were in the top of the forest, looking out and down.

From above, the roof structure is visible; it uses indigenous materials and techniques -- tiles, arches, barrel vaults -- that journeymen builders might employ on smaller buildings. Here, they are carried aloft and made magnificent by the use of architectural steel that will be hidden in the tree-like branching of the columns.

Unlike any other architect's work, the shapes of Gaudí's ornaments are distinctively organic. Carved of stone or cast in concrete, every one serves some functional or structural purpose, but from "within" the building, on the lower bridge between the two great eastern spires, function is less obvious than the delightful originality of the shapes. It is here that I get the sense of bring a part of the structure myself, along with these other climbers and the workmen below. The vision may not be fully elaborated, but the Maestro, Gaudí, surely imagined this building just as it is today.

Climbing down, we could see back up toward the spire-tips, out over the worksite, down to the bridge between spires: the whole magnificent carapace of the church is revealed to us. We remember Gaudí's dictum: "If well planned, structure becomes ornament and additional ornament is unnecessary." We see how the "scales" of the tower direct the rain out and the wind in to cool the stairway, how the steps and inner and outer skin of the spire work together to give it form and rigidity. Not a stone is wasted.

Below us, we see other climbers taking pictures and gawking at this extraordinary structure. They've got the same spirit of wonder that has taken hold of us, and our shared explorations are good spirited. Missing a picture on a narrow stair, I go down, squeeze past them on the narrow bridge, and climb back up again to find the perfect angle ...ah, yes, there it is. From here I can look between the scales right across at the top of the east facade...

On the bridge again, I can look up at strangely unfamiliar "Gaudí shapes" decorating the pointed tops of arches on the facade and spires towering now far above me. See: it says "Sanctus Sanctus" again and again around the spire bases.

Below the spires, windows on the inner side of the spiral stairway open on the nave of the church right at the level where the columns branch. Gaudí's genius, adapting shapes originally found in nature to innovative materials and designs, manifests here in column designs that look more organic than mathematical, although we know from his models and drawings just how carefully he had worked out the mathematical details.

At ground level, I wandered back through the nave awestruck by the magnitude of this work, and the amazing completeness and flexibility of Gaudí's vision ...and the flexibility and dedication of the architects and craftspeople who carry the work on, elaborating their work from a few sketches, elevations, models ...and, luckily, a true understanding of the Maestro's vision. So the work crawls on.

Enough of the nave is finished now so that it was easy to get a sense of the way the church will appear when it is finished -- as if the congregation is on the floor of a stone forest, massive trunks surmounted with branches that in turn support the canopy.

I left the church with my heart beating fast, and sat and watched the play of light on the western facade, digesting the starker vision of the west facade. The Maestro redesigned it despite his patrons' complaints after he nearly died of a dire illness. "I will sacrifice the work," he said, because he sensed that his new vision would make the facade at once truer and more approachable.

This amazing church is both the collaboration of generations of skilled workers, and the inspired vision of one man -- unusual in such a large church, yet undoubtedly more fitting for our age. I wonder how its story will be told, and who will be remembered, half a millennium from now.

Just as the sun poured its last beams on the western facade, I walked out and was dazzled. The golden stone and colored concrete presents a starker vision at this end of the church, which Gaudí redesigned after a brush with serious illness. At one end, the miraculous birth, and at the other, a portrayal of the human aspects of the Christian experience, love, search for understand, death, and the hope for resurrection.