Hometowns forget us quickly when we leave them, even if some of the people left behind do not. Architecture, infrastructure and whole communities can change with scant warning or regard for our memories, or our bearings when we return. When you go home again — and you can, contrary to the popular adage — even what you remember has to be reintroduced to you; sidewalks once accustomed to your footprints have to be broken in again, like a new pair of shoes. For Felice, an unmoored Italian expat visiting Naples after a four-decade absence, it’s not what he recognizes of his home city that brings him comfort, but the new, younger life surging past the ghosts that kept him away so long. “Nostalgia” is thus a barbed title for Mario Martone’s gruffly lyrical urban portrait: Sometimes you need to go back, the film says, but it’s best to keep looking forward as you do.

Unlike his brooding protagonist, Neapolitan son Martone can scarcely stay away from the city known for its world-beating pizza and, less appealingly, the much-documented exploits of the Camorra crime syndicate. His cinema has been heavily consumed with the city’s historical and cultural fabric, up to and including last year’s regional theatrical biopic “The King of Laughter”; hopping briefly across the water to an adjacent island, 2018’s “Capri-Revolution” counted as a relative vacation for the filmmaker. If much of Martone’s recent work has been turgid or opaque, seemingly limited to local audiences in its appeal, the atmospheric, elegiac “Nostalgia” reverses that trend, even as it devotes itself wholeheartedly to Naples’ grimy streets.

The director’s first film in 24 years to unspool in Cannes — Venice, unsurprisingly, has since been his go-to festival — benefits from a contemporary, outward-looking sensibility, as befits its hero’s conflicted native/stranger perspective, that identifies a universal kind of heartache in his homecoming. This is especially true of “Nostalgia’s” lovely, laconic first half, in which fiftysomething Cairo resident Felice (Pierfrancesco Favino) touches down in Naples and slowly, silently rediscovers its streetscapes and soundtrack, his backstory unfolding through fragmented sensory detail and the wordless dialogue of simple human touch. The spell is broken somewhat as things get more vocally explicated, and “Nostalgia” shifts into the familiar, less arresting register of Italian underworld drama; still, it remains evocative and absorbing.

“I’m sorry I don’t remember you,” says Felice upon being recognized in a local restaurant by an old family friend, and it’s not so much an apology as an expression of personal regret. After arriving in Naples and checking into an identity-free vacuum of an airport hotel, he heads into town and wanders the streets of his childhood neighborhood, seemingly willing himself to feel more at home than he does. Even his actual home is no longer accommodating: Expecting his elderly mother Teresa to answer when he knocks on the door of the family apartment, he instead finds surly strangers claiming the space.

Teresa (Aurora Quattrocchi, excellent) has instead been cajoled into taking a dark, narrow basement studio several floors below; not much longer for this world, she shrugs off the downgrade as her long-absent son seeks better digs for her, working out layers of guilt through real estate. And, occasionally, through more direct gestures, as in one achingly moving scene where Felice gives his frail, inflexible mother a delicate sponge bath over her initially prim protests, the duty of care having shifted irrevocably from parent to child.

It’s for Teresa that Felice has returned, and even then only under duress from his Egyptian wife Arlette (Sofia Essaidi) back home. Having left Naples at 15 — under seamy circumstances gradually revealed in Super-16 flashback — the younger Felice had never intended to come back. Yet the longer he stays past his initial obligations to his mother, the less able he finds himself to leave these simultaneously intimate and alien streets, lined with perspiring ochre apartment buildings and scored to the incessant, obnoxious neeee-yawwww of men on motorcycles. Felice buys one himself, retracing the urban biking routes of his youth, with editor Jacopo Quadri’s elegant match cuts linking past and present along these concrete circuits.

With his jaw ever-set and his brow ever-furrowed, the stoically charismatic Favino is the right human anchor for this project: sympathetic in a strong, silent way, but equally capable of melting into the film’s busy, shadowed tableaux of urban unrest, shot in tanned, tone-on-tone style by DP Paolo Carners. There’s an aptly nostalgic, Polaroid-soft finish to the flashbacks, but the visuals cool as the older as Felice faces the heavier baggage of his past, setting out to reunite with Oreste (Tommaso Ragno), a boyhood friend turned vicious crime boss. He continues this pursuit over the advice of community-minded priest Don Luigi (Francesco di Leva), whose bright-eyed teenage charges give Felice renewed hope for the city he once wrote off.

More in line with Martone’s 2019 Camorra saga “The Mayor of Rione Sanita,” these schematic, even sentimental, narrative developments set “Nostalgia” on a very different course from the observational, asphalt-textured geographic storytelling of its opening reels — until an unexpectedly brusque, restrained ending once more leaves viewers adrift in Neapolitan alleys. Even in its more generic stretches, Martone’s latest feels both inviting and convincingly inhabited, a siren song to the past that confronts us with a violent, unromantic present, paved under with the same old, blood-washed cobblestones.