For anyone familiar with the springcleaning jetsam of a garage sale, the Marché aux Puces in Paris offers a cornucopia of delights. It is bigger and weirder, at once more general and more specific than the local thrift shop or church rummage sale. For three days a week, you can sift through keys for giant forgotten locks, dig into boxes of individual chandelier crystals or flip through paintings—some bad, some brilliant. Only a fool goes with a shopping list.

In his 1928 novel, Nadja, the surrealist artist André Breton described the Marché aux Puces as “an almost forbidden world of sudden parallels, petrifying coincidences, and reflexes particular to each individual. . . flashes of light that would make you see, really see.” Later, in Mad Love (1937), he recounted a walk there...