"Is there actually a town and a street like this?"

"Oh, yes; a street with houses, trees, and lawns precisely like that, right down to the last blade of grass and the wicker baby-carriage on the porch. You've seen an aerial shot of it; it's called Winfield, Vermont." Rube grinned at me. "Don't get mad," he said gently. "You have to see it before you can understand it."

We walked on, high up on the spider web under the humming machinery and just above the hundreds and hundreds of lights. We crossed directly over the house with the man on the porch, and it was strange to think that if he should look up here from his paper he wouldn't see us but only an apparent sky. He didn't look, though; just continued reading his paper until the eave of his porch roof cut him from view. Angling to the left onto another length of catwalk, we passed over a wall and the area was gone from sight.

It was instantly cooler, with a hint of dampness and a feel of rain, and we stopped to stare down. Far below lay a section of prairie and through it ran a tiny stream. On the other side of the area from where we stood grew a scattering of thin white-trunked birch trees. These were stragglers at the edge of a much thicker woods which stretched up and over the crest of a rise. Most of the woods, I realized now, was painted on a wall but it looked very real. Almost directly under our feet stood three tepees made of hide and daubed with faded circles, jagged lines, and sticklike figures of men and animals. A thin smoke drifted from the open top of each tepee. Before one of them a puppy lay tethered to a peg; he was worrying something held between his paws. As we stared, some of the lights aimed into the area went off one by one — we could just hear the clicks — and the triangular shadows of the tents slowly deepened on the grass of the prairie, and now we could see an occasional spark in the trickles of rising smoke.

"I love this one," Rube murmured. "Montana, about sixty miles from where Billings now stands. There are eight people — men and women and one child — in those tepees; all of them full-blooded Crow Indians. Come on."

In our felt boots, moving almost soundlessly on the narrow metal grill, we walked on across space, again crossing over a wall. We stopped high above a triangular-shaped area and stood directly over its shortest side facing ahead toward its farthest point. A white stone building rose from the floor almost to our feet. Again, it wasn't what it seemed from its front and one side; there were only two walls, supported at their backs by iron-pipe scaffolding. Extending outward from the base of these walls lay a rough stone pavement. Between the cracks of the pavement four men in overalls were planting narrow strips of sod and little clumps of weeds which they took from baskets. The rough slab paving ended in a short grassy slope which led down to what seemed to be an actual river. Water flowed there, brown and sluggish, moving along one side of the triangular area toward its point, off ahead.

Something about this pseudo building of white stone, which ended only a yard or two under our feet, was becoming familiar, and I walked on along the catwalk to where I could get a better view of its front. The side wall along which I walked was flying-buttressed, and then I saw that the front rose into twin square towers. From the sides of the towers projected carved stone figures; one was nearly close enough to reach down and touch. The figures were winged gargoyles and the buttressed wall and twin towers were those of a cathedral; this was Notre Dame of Paris; now I recognized it from movies and photographs.

Watching my face, Rube saw that I understood what we were seeing, and now he pointed across the river. I saw winding dirt roads trailing off into the distances of the other side; a few score of low wooden or stone structures; most of the area was farmland or woods. "Medieval Paris in the spring of 1451." Rube smiled. "It will be, that is, if we ever get the damn thing finished." His arm lifted, his forefinger pointing again, and now, across the river and far ahead, I saw a man in tan cotton pants and blue work shirt streaked with paint — a giant standing before houses and trees that reached no higher than his knees. A palette lay on his left forearm, and he was carefully painting in an extension of the forest, drawn in charcoal on the area wall on the other side of the brown, slow-flowing Seine. "Hell of a lot more work to be done here," said Rube. "Every stone of the cathedral to be aged with acid washes and stain; after all, in 1451 it was already several centuries old. In a sense this is our most ambitious project, but I doubt if even Danziger really thinks it can work. Ready? Let's move on."

Without stopping we walked over an empty area roughly rectangular in shape, one end a little wider than the other. Far below two men on hands and knees were marking off the area with strips of cloth tape and with colored chalk. "I don't quite remember what's going in here," Rube said, "but I think it will be a field hospital of the AEF near Vimy Ridge, France, 1918."

We looked down at a section of a snow-covered North Dakota farm in the dead of winter of 1924. The air over it was sharply cold; within half a minute we were shivering. We stood over a Denver street corner of 1901; it included a cobbled street with streetcar tracks, and a little grocery store with a tattered awning, into which two overalled men were wheeling supplies. Leaning on the rail beside me Rube murmured, ''Reconstructed from seventy-odd photographs and snapshots, including one magnificently clear stereoscope view. Together with Lord knows how many present-day, on-the-site measurements. We're not finished yet; they're stocking the store now, everything absolutely authentic to the time. When it's done, it'll be the way it was, you can be certain of that." He glanced at his watch. "There are a few others, but it's time to meet Danziger now." We turned to walk back, Rube just behind me. "And our New York site doesn't need to be duplicated; we'll catch that after lunch. You hungry? Confused? Tired and irritable?"

I said, "Yeah, and my feet hurt."

We ate in a small cafeteria on the sixth floor, a windowless fluorescent-lighted room tiled in pale blue and yellow and not very much larger than a big living room. Danziger was already waiting, seated alone at a table. As we picked up trays he waved to us; on the table before him stood a piece of apple pie and a bowl of soup covered with a saucer to keep it warm. Rube and I slid our trays along the chromed rails. I took a glass of iced tea, and a ham-and-cheese sandwich from a stack of them already made up and wrapped; Rube had Swiss steak and mixed vegetables, served up by a nice-looking girl. There was no cashier at the end of the rails, no charge, and Rube picked up his tray, said he'd see me later, and walked over to join a man and a woman just starting to eat. I carried my tray to Dr. Danziger's table, looking the place over as I walked. There were only seven or eight people besides us, with room for about a dozen more, and as I stood unloading my tray after speaking to Danziger, he guessed what I was thinking and smiled.

He said, "Yes, it's a small project. Maybe the smallest of any importance in the history of modern government, a pleasing thought. We have only about fifty people who are fully involved; eventually you'll meet most of them. We can and do occasionally draw on the services and resources of various government branches. But we do it in a way that doesn't suggest what we're up to or arouse questions." He lifted the saucer from his bowl of soup. "No chocolate pie today, damn it."

He picked up his spoon and sat watching me unwrap the sandwich I didn't really want. I was too tense to feel like eating; I'd have liked a drink. He said, "We maintain secrecy not by stamping things 'Classified' and wearing lapel badges but through inconspicuous-ness. The President, of course, knows what we're doing, though I'm not sure he thinks we do. Or that he even remembers us. Unavoidably we're known to at least two Cabinet members, several members of the Senate, the House, the Pentagon. I could wish that somehow even that weren't necessary but of course they're the people who get us our funds. Actually I can't complain; I make my reports, they're accepted, and they haven't really bothered us."