The most significant acts of espionage in history took place at the close of World War II in Santa Fe.

True, the roots of the atomic-spy story are in Los Alamos and dozens of other places, but Santa Fe was where the brilliant but philosophically tortured physicist Klaus Fuchs turned over the secrets to the atomic bomb to bread-for-the-masses, traveling communist Harry Gold 64 years ago.

Many local places figured in the Manhattan Project in general and the Fuchs-Gold story in particular. Here is a tour of some of the landmarks:

• The tiny room at the back of a Sena Plaza alcove between 107 and 109 E. Palace Ave., now an office for The Rainbow Man, served as the Santa Fe headquarters for the Manhattan Project during World War II. Scientists drafted into the secret project usually arrived by train at Lamy and were taken by car to the office, where an efficient secretary named Dorothy McKibben greeted them, gave them their papers and made arrangements for them to be driven to Los Alamos. She warned them not to tell anyone what they were doing or even that they were physicists, and reminded the more famous ones to use false names in Santa Fe. A plaque at the back of the alcove commemorates the once-secret office.

A plaque at the Manitou Galleries, 123 W. Palace Ave., falsely claims that building was the site of the war-time office.

• Manhattan Project personnel got mail at P.O. Box 1663, Santa Fe — a postal box at the Santa Fe Post Office, now the Museum of Contemporary Native Arts, 108 Cathedral Place.

• Project director J. Robert Oppenheimer and many of the top scientists spent much of their time in Santa Fe at the bar of La Fonda, 100 E. San Francisco St., under the discrete watch of government agents. Despite the strictest military secrecy from 1943 to 1945, most Santa Fe residents were aware of the weapons project on "The Hill."

• 130 W. Water Street, which today houses the Coyote Cafe and several retail shops, was the main Santa Fe bus station when Harry Gold first arrived on June 2, 1945. It was time of great hope and apprehension. Germany had surrendered less than a month earlier, but Japan remained at war. Gold had come to Albuquerque by train and taken the bus to Santa Fe. He walked to the Plaza and picked up a map of the city at a tourism office in the Palace of the Governors.

The 35-year-old Philadelphia bachelor had been won over to the communist cause as a chemistry student at Xavier University in Cincinnati because, as he put it, he felt sorry for the Russian people. In 1935, he began working secretly for the Soviet trade office in New York City. His first "industrial espionage" jobs were to report on modern sugar processing and the extraction of vitamins from fish oil. Gold reasoned he was not stealing from his country, but from the capitalists. He took cash for his moonlighting. He was not the best spy, mixing espionage with other business and letting evidence build up in the apartment he shared with his father. Years later, as FBI agents searched his home, the Santa Fe map fell out of a book, prompting Gold's first confession.

• Gold probably walked by the secret alcove on Palace Avenue on that Saturday afternoon in June as he made his way to the Castillo Street bridge across the Santa Fe River, where he was to meet with KlausFuchs. Today's Paseo de Peralta bridge replaced the Castillo Street bridge when the Paseo de Peralta "loop" was built in the 1960s. If you want to see what the bridge looked like when Gold met Fuchs, continue walking upstream to the Delgado Street bridge — a low, unassuming, concrete-form bridge that was built at the same time.

Fuchs arrived from Los Alamos about 4 p.m. driving his Buick — one of a handful of private cars in Los Alamos at the time. His first meeting with Gold, whom he knew only as "Raymond," had been arranged by Fuchs' Soviet contacts in England.

The two men's paths had crossed before. Shortly after Fuchs arrived in the United States, he waited on a New York City street corner, carrying a book with a yellow cover, as instructed. Gold was carrying a package wrapped with brown paper and a string. They took the subway to the next stop, then got off and began to talk. They lost touch when Fuchs suddenly was sent to Los Alamos in early 1944, but Gold was able to contact him again through Fuchs' sister and arrange to rendezvous in Santa Fe.

Fuchs, then 34, was a rare type of ideological spy. Most do it for money. But when one of Fuchs' contacts tried to pay him, he was offended. Born in Germany, a son of a Lutheran theologian and his wife who committed suicide when Klaus was 19, Fuchs became a communist as teenager. In 1933, as the Nazis cracked down on leftists, he left Germany to study physics in Scotland and England, where he joined a secret cell and began to meet with Soviet agents. As Fuchs advanced as a physicist, he was drawn into Britain's early atomic-bomb project called "tube alloys." When the United States entered the war, he was naturalized as a British citizen so he could join the British delegation to the Manhattan Project.

In Los Alamos, Fuchs thrived. He quickly became one of the project's top physicists. When Edward Teller turned his attention to the "super" or fusion bomb, Fuchs took over the calculations on the plutonium-implosion device. A bachelor, he could be counted on to escort single women to dances or to baby-sit when a young couple had a rare chance for a night out. Fuchs would later write that he compartmentalized his professional and communist life: "Looking back at it now the best way of expressing it seems to be to call it a controlled schizophrenia."

Fuchs' meeting with Gold in 1945 at Santa Fe's Castillo Street bridge went quickly. Fuchs handed over a packet of documents describing the design for the plutonium-implosion device, said he would be too busy to meet again that summer — something would happen soon — and made plans to meet Gold again on Sept. 19. Then Fuchs drove back to Los Alamos. Gold caught the bus back to Albuquerque.

• After spending the night at the Albuquerque Hilton — later La Posada de Albuquerque and now Andaluz, 125 Second St. NW — Gold walked to a small apartment complex at 209 High St. NE. David Greenglass, a 22-year-old Army sergeant working as a machinist in Los Alamos during the week, and his wife, Ruth Greenglass, rented the second-floor flat. When David, the younger brother of Ethel Rosenberg, answered the door, Gold announced, "I come from Julius" and handed over half of an "Imitation Raspberry" Jell-O box top. The other half was in David's wallet — a recognition signal that he said was devised by his brother-in-law Julius Rosenberg earlier that year after dinner at his apartment in Manhattan's Lower East Side. According to Greenglass, Rosenberg had snipped the box apart with scissors, quipping, "The simplest things are the cleverest."

The Greenglasses had been expecting the courier for weeks. In May, Ruth had twice waited, as instructed, at a Safeway at 520 Central Ave. SE, but no one showed up. On the Sunday morning in June, David Greenglass told Gold he needed time to prepare his report on how to make an atomic bomb. Gold walked to the railroad terminal at 414 First St. SE, checked the schedule and watched a Catholic procession before returning to the apartment to pick up an envelope of documents from Greenglass. Gold handed over $500. That evening, he caught a train back East carrying two packets: one from Fuchs and one from Greenglass.

Things began to move quickly that summer. Early on July 16, Fuchs was among those at Trinity Site in the Jornada del Muerto to watch the world's first nuclear detonation via a plutonium-implosion device nicknamed "Fat Man" after British Prime Minister Winston Churchill. On Aug. 6, a uranium-fueled, gun-type gadget — originally called "Tall Man" for President Franklin Roosevelt, then changed to "Little Boy" when its barrel was shortened — hit Hiroshima, Japan. President Harry Truman immediately announced Los Alamos' existence to the world. On Aug. 9, a plutonium-implosion device hit Nagasaki. The Soviet Union declared war on Japan that same day. On Aug. 15, Japanese Emperor Hirohito announced surrender. A formal surrender took place aboard the USS Missouri on Sept. 2.

• On Sept. 19, Harry Gold returned to Santa Fe by bus. This time, feeling flush with cash or just short on time, he had flown to Albuquerque. Fuchs and Gold had agreed to meet at what they described only as a church on the north side of downtown — probably the Scottish Rite Center at 463 Paseo de Peralta. Early that evening, Fuchs arrived in his Buick with its back seat filled with liquor purchased for the going-away party for the British delegation.

This time, Fuchs had pulled his Buick off the road between Los Alamos and Santa Fe to write out, in longhand from memory, production figures for enriched uranium at Oak Ridge, Tenn., and plutonium at Hanford, Wash. He gave the data to Gold. Then the two men drove into the mountains, parked where they could see the lights of Santa Fe and began to talk about the post-nuclear world. It was one of the few times either dared open up. Although it is not recorded, it is likely they had a few drinks. Both were heavy drinkers. Fuchs held his liquor well, but Gold, when drunk, would make up stories about being an identical twin. Later that evening, Fuchs dropped Gold off at the Plaza. Fuchs drove back to Los Alamos. Gold took the late bus back to Albuquerque and caught another commercial airliner back to Philadelphia. They never met again.

The story began to unravel after Aug. 29, 1949, when the Soviet Union detonated its first atomic bomb, "Joe One," in Kazakhstan. Tests downwind indicated it was a plutonium-implosion device like Fuchs had worked on. Some already were suspicious of him. One of his early reports on fission weapons had turned up in a decoded Russian transmission. But Fuchs, now back in England working in the Harwell nuclear facility, seemed to want to confess. In early 1950, Fuchs went to Scotland Yard in London, hoping to trade information about his secret contacts to mitigate the damage he had done and for help in getting his father, now in East Germany, into the West. Instead, Fuchs was arrested. "Do you realize what this will do to Harwell?" he gasped.

Fuchs' confession exposed the Santa Fe connection with Gold. But something didn't quite add up. A ticket stub found in Gold's apartment indicated he got off the train in Albuquerque — not Lamy where Santa Fe visitors usually disembark. That led Gold to confess he also met with the Greenglasses in Albuquerque. David Greenglass agreed to testify against his sister and brother-in-law in exchange for a 15-year sentence for himself and no charges against his wife. The Rosenbergs, who refused to name others involved in the conspiracy, were convicted at trial in 1951 and electrocuted on June 19, 1953. In retrospect, the death sentence — the first for treason in peacetime for the United States — seems unwarranted. David Greenglass' drawings, which the Rosenbergs helped funnel to the Soviets, was insignificant compared to what Fuchs supplied — as well as misleading. The crude drawing of the plutonium-implosion device incorrectly identified its fuel core as enriched uranium.

Gold, who was sentenced to 30 years in prison, was paroled in 1966 and died in 1972. Fuchs, who spent nine years in an English prison, talked about going to a neutral country, like India or Brazil, upon his release. But after a 1959 prisoner exchange with the Soviet Union, he resettled in East Germany, married a woman he had known since his youth and returned to nuclear research. Although he traveled widely in the Eastern Bloc on government-sanctioned campaigns for disarmament, he never again sat foot in the West. He died in 1988. David Greenglass, who was released in 1960, is the only principal in the spy story still living, most recently in a Long Island suburb.