Navigating the sonic labyrinths of Bon Iver is integral to accessing i,i, their fourth studio album.

Why not take a leaf out of In Praise Of Walking, a book by Irish neuroscientist Shane O'Mara? He advocates regular strolling, which he believes can unlock the cognitive powers of the brain, essentially making one smarter, happier and healthier.

So, put on your earphones and amble along. Give in to the rhythm, feel the melodic contours and rise and fall in sync with frontman Justin Vernon's morphing voice.

That is probably the most apropos way of experiencing these 13 songs, which complete the band's seasonal quartet of albums - starting with the lonely, wintry debut of 2008's For Emma, Forever Ago, traipsing through the spring travelogues of 2011's Bon Iver, Bon Iver and exploring the summery, digital phantasmagoria of 2016's 22, A Million.

This is the autumnal stage of a sojourn, which ends in an introspective i,i. There are tricky, jarring shards, which were first heard on 22, A Million, but there are less splinters, yet more illuminating glances.

Take the first song, Yi, a 32-second mutation of a phone recording of Vernon in a barn switching a radio on and off and him uttering: "You recording Trevor?"

Perchance the title is a mondegreen of the word "yeah" at the start of the sample or does it refer to the Chinese word for the number "one", as a Reddit comment suggests? Or is this all coincidence?

For sure, the happenstance feel foreshadows the collagist approach for the rest of the album. Vernon is constantly redrawing the perimeters of the Bon Iver sound, eluding the indie-folk label thrust upon them from the offset.

Yi segues into iMi (a neologism meaning "I am I"?), a gorgeous ballad alive with gas hissing, mutating horns and a rotation of at least five vocalists, including English musician James Blake and Vernon.

"Living in a lonesome way/Had me looking other ways/'Cause I am, I am, I am lost here, again," Vernon sings, before the rest come in - one by one - in a communal declaration.

A similar restlessness infuses Holyfields, - with the comma at the end of the title signifying the continuity of hope or despair. A ceaseless whirring of synths and keys circle above as Vernon appears to address working-class folk trying to make ends meet.

"Coming in very late/Just above our pay grades," he sings, switching between falsetto and a normal chest voice. "Stay, go?/Better that you find a new way."

In the gospel-tinged U (Man Like), he invokes a community, including American singer-songwriter Moses Sumney and the Brooklyn Youth Chorus, over a piano riff delivered by Bruce Hornsby.

"How much caring is there of some American love/When there's lovers sleeping in your streets?" is his wake-up call in a divided United States.

One's ears perk up when he is front and centre in Hey, Ma, one of the album's highlights. "Full time, you talk your money up/While it's living in a coal mine," he confronts, while holding out for redemption.

"Tall time to call your Ma," he beseeches, drums marching softly over synths echoing in the chamber of one's heart.

By the time one comes to the last track, RABi, Bon Iver has come full circle.

"Well, it's all just scared of dying/But isn't this a beach?" Vernon asks in an oddly moving non sequitur. He peers at his past and angst-ridden self from afar, and nudges him to appreciate what he has.

The guitar is plucked softly. Synths circle like mist. He is home, finally, here, nowhere, everywhere.