I’m on Cleethorpes beach, and for a time I think I’m standing at a single boundary. But when I cross it, another one appears. It turns out that I’m traversing a sequence of boundaries – in place, and time, and culture, and autobiography.

In the first instance it’s a physical boundary, but not one marked by a fence. It’s the point where the seafront separates into two different kinds of place.

North of the boundary are the central, most popular sections of the beach and promenade. In the summer here are the donkey rides, the sandcastles and the pier; immediately behind them, up on the road, the busy hotels, bars and chippies. On the first warm day of the year this space bustles with trippers; today it’s overcast, blustery and close to freezing, but there’s still a generous sprinkling of human life.

South of the boundary the landscape and mood alter abruptly and substantially. The beach is enveloped by a densely vegetated saltmarsh. It’s divided from the coastal road by a mesh of dunes and thickets. There’s an ornamental lake and a narrow-gauge railway, an observatory, a gallery and a Chinese restaurant. Seldom more than sparsely peopled, today it borders on desolate.

The boundary is neither natural nor fixed. It’s marked by the edge of the saltmarsh, but this moves forward and back. Anxious to retain the tourist shilling, North East Lincolnshire Council regularly deploys machinery to churn up any vegetation that crosses the threshold, thus maximising bucket-and-spade space. Equally concerned to defend the rare birdlife that has made a habitat of the saltmarsh, Natural England has declared it a Site of Special Scientific Interest, to hold the line against the council’s southward assault.

The battleground switches to the local media. Councillors warn of economic meltdown. Letters appear from readers. The word encroaching is used a lot. Negotiations occur. The boundary shifts, and the boundary shifts. A few steps one year, 30 metres the next.

Today I’m walking with my mum, who still lives a short distance from the beach. We recall – dimly, in my case – a chain of huge concrete cubes placed here some decades ago, perpendicular to the shore, to stifle the action of longshore drift, we think. They’re buried now, below where we stand. The sand has accumulated against the sea wall instead. Of the steps down from the road to the beach, likewise, only the uppermost remain above the sand. Since we visited here in my childhood the entire level of the beach at this point has risen by at least a metre and a half.

Another shift over that time has been in the mindset of local people. In the winters of the 1970s and 80s, my mum says, even on fine days, the seafront would be entirely depopulated. You just didn’t go to the beach for half of the year. You just didn’t, because nobody did.

Just across the road from the beach is the former site of Cleethorpes Winter Gardens. As well as a significant venue on the rock, northern soul and house scenes, its modest art deco leanings made it one of very few distinctive buildings in the area. The council demolished it in 2007, then left the site derelict for the best part of a decade before the appearance of some dull apartment structures.

Opposite them, protruding into the beach at the boundary of the saltmarsh, stands Cleethorpes Leisure Centre, built in the 1980s from brown Perspex, or Lego, or milky coffee. Viewed from a distance it could be a modernist fire station, or a small nuclear reactor. A chute protrudes from the side of the building and back in, giving swimmers in warm, chlorinated water a glimpse of the chilly saline alternative outside.

In its way this site also marks a cultural and temporal boundary, between different concepts of pleasure and models of society.

Since a zenith in the 1970s, the messy hedonism of the communal music experience has undergone a slow fadeout, while in its place, perhaps, has arisen the pursuit of physical fitness as a form of recreation – Thatcherite in its intensity, its individualism, and its basis in self-‘improvement’. And the lost world my generation was born into – smoky and haphazard, tolerant of brutality and bigotry, but ebullient and somehow wide-eyed amid the dysfunction – is built over with an increasingly ordered and joyless present, where social and technological progress is stalled or in retreat.

Today is the day after boxing day: we’re at the boundary between 2017 and 2018. This time last year I undertook a similar walk. Alone, in clear, mild conditions, I turned my back to the sea wall and walked out through the breadth of the saltmarsh to its far side.

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The distance from land couldn’t have exceeded a kilometre but the shifts in the landscape and its sensations were unexpectedly profound. Textures and light were softer. The sand seemed set down gently, granular like a fresh snowfall, or demerara sugar. Driftwood was as smooth to the touch as the limbs of an infant. Pale violet striations unfurled across a limitless sky, as if projected from the fine lined patterning of the dainty, fingernail-shaped shells that crunched at my feet.

In the run-up to Christmas 2016 I’d been affected quite badly by stress. It dissipated during that walk. The issues at work that had occasioned it have not touched me in the same way since. Without realising it at the time, I was at a boundary between sickness and well-being.

Today we continue south a little way, winding around the lake and drifting in towards the surprising new developments on the southern boundary of the town: empty fast food halls and clothing retailers; an incongruous Premier Inn, more southern Europe than south bank of the Humber. At my mum’s suggestion, we start up a track beside Buck Beck. I’ve never come this way before. Trees are silhouetted against a sky candy-striped by early dusk. The track is too sodden to progress. At length my mum turns home. I clamber a muddy bank to look at a building site, sip a bit of whisky, warm my hands and ponder my next direction.

A fox is watching me.

I’m startled. She’s wary, but unruffled. The two of us hold eye contact for a time. Then she trots away, at once still circumspect but beautifully nonchalant, light-footed, keeping me in corner-sight. For some minutes I follow at a distance. Then I let her go. In my pocket there’s the hip flask and a big clam shell I picked up an hour ago, and between them there’s just enough space to put a sense of enchantment.

When I look up I’m close to the point where the Greenwich meridian passes through Cleethorpes: the boundary between the eastern and western hemispheres of the Earth.

I press back towards the estuary along a section of Buck Beck, illuminated only by the rising moon; into the Thorpe Park complex of chalets and static caravans, eerie in its near-abandonment to the dead of winter; over the dunes and up into the saltmarsh, where a text message reaches me from a friend who’s already returned to work after Christmas and is now emerging into rush hour in the city. It’s like a voice from another world.

Maddeningly, a closed footpath forces me to backtrack. Emerging from Thorpe Park, my thoughts return to the fox. As if in response, from nowhere, there she is again, darting across the main road, through a halogen-steeped car park and disappearing into undergrowth.

In the end I’ll return to the central promenade and neck a pint of strong ale at Willy’s bar, just above the lifeboat station. I’ll eat a cone of chips and curry sauce, strolling up St Peter’s Avenue as the temperature dips to zero. I’ll discover a passageway called Cuttleby which I’ve never noticed before, joining two streets on the walk back to my mum’s house. And, like the other places I’ve seen on this walk, it will remind me that it’s possible to spend the first 20 years of your life in a town and, on returning, still run into vast areas of terra incognita when using a mental map to navigate it.

In 2011 I travelled down the east coast from Northumberland to Yorkshire so that I could start to join it up in my mind. Today I resolve (not in a new year’s way, just in a way) to come back and undertake a similar belated journey south out of this place, along the coast of Lincolnshire, prompted by this walk which has straddled the boundary between familiar and unknown, between memory and discovery.