Although for a time he helped organize the annual parade in Manhattan celebrating Israel, he conducted a two-hour interview in 2003 in Gaza with a leader of Hamas, Dr. Abdel Aziz Rantisi, who had just survived an attack by Israeli helicopters.

The book of his that broke important new ground was “Against All Odds.” In writing it he interviewed 380 Holocaust survivors and found that, far from the pathological stereotypes surrounding them, they had more stable marriages, equivalent economic status and a lesser need to seek psychiatric help than other American Jews of the same age.

He argued that traits like adaptability, tenacity and resourcefulness, which had been needed to endure near starvation, terror and the loss of so many loved ones, had enabled most survivors to flourish in the freedom and opportunities that America afforded. The book won an award from the Jewish Book Council.

What made his ramble through New York so beguiling — besides the sheer feat of his feet — were the serendipitous encounters and discoveries of offbeat corners of city life. In Bensonhurst, Brooklyn, he met a man whose ample garage was chock-a-block with old Dodger baseball uniforms, carousel horses, gaudy amusement arcade machines and vintage cars — all as a wistful homage to the Brooklyn of his childhood.

In Gowanus, Brooklyn, he came across a long-dormant grocery on a street of rowhouses and found that it that had been kept as a shrine by the descendants of a Neapolitan immigrant who had opened the business a century before, its Rheingold and Schaefer beer neon signs flashing at Christmastime in tribute.

“I saw this as a remarkable example of filial piety, something that today’s generation might not understand,” Professor Helmreich told Mr. Mitchell. “Today’s generation is much more techie, much more involved in the present.”

Image Professor Helmreich’s rambles through New York were inspired in part by a pastime that he and his father called “Last Stop.” They would choose a subway, take it to the end of the line and spend a few hours exploring the novelties of neighborhoods they had never seen. Credit... Alessandra Montalto/The New York Times

William Benno Helmreich was born on Aug. 25, 1945 in Zurich. His parents, Leo and Sally (Finkelstein) Helmreich, had met in Nazi-occupied Belgium and had spirited their way through France into neutral Switzerland. In 1946 the family emigrated to the United States, where his father worked first repairing diamond jewelry and eventually became a diamond dealer.