Some of their names are famous the world over — Bondi, Coogee, Maroubra — but for Sydneysiders, the city beaches aren’t just tourist destinations to daydream over, they are our outdoor lounge rooms.

And we trek from all over town to relax or revive there. On a midweek evening, you’ll find refugees from city offices ditching the ties and heels to cool off before heading home.

First thing in the morning, you’ll see the local surfers making the most of a good offshore breeze and the runners putting in the hard yards in the soft stuff high on the beach. Not to mention the yoga class or group training crowd up on the grass.

But it’s on the weekend when Sydney arrives in numbers, especially on weekends like this one, when temperatures are forecast to go as high as 45 degrees in Western Sydney.

As many as 100,000 people will swarm to the three big municipal ocean beaches. Packed buses stagger in from the burbs and carparks fill up early as we arrive from all points west — inner-west hipsters, students from Parramatta, young couples from Blacktown, or families from Penrith.

It’s that mass of humanity that attracts photographer Paul Blackmore, who has been documenting Sydney’s city beaches for years. He loves the quiet beach of the morning or evening but relishes that different beast of the day.

“There’s the other beach when it heats up and the crowds come — that’s a sort of sensual overload,” Blackmore says. “There are just bodies and a mass of people and it’s a different experience.

“When I think of the beach, I think of different things … in the morning, that sort of beauty of it, and as it heats up there’s that sort of kinetic craziness that is the crowds and the people and the heat.”

Blackmore, who has worked around the world for more than 20 years, reckons the city beach is where Australian culture is “laid bare”.

“For me, the beach is like one of the few great Australian public spaces,” he says.

“Europe has its squares and gardens but, for us, the great Australian experience is sort of played out on the beach and it’s who we are and our culture is laid bare ... You get to see that sort of intensity and energy and the beauty in public like that.”

Blackmore’s evocative images, featured online on Instagram and in his soon-to-be-published book Heat, will be familiar to any Sydney beachgoer.

There are lithe teenagers jumping off rocks into the surf, hundreds of sunbakers crammed onto baking concrete at Clovelly or the lone swimmer leaping through a breaking wave with one arm breaking the impact.

Blackmore’s photographs are very modern but the world he captures is almost classic — one that would be easily recognised by Sydneysiders from decades ago.

The same thing works in reverse. If you look at the work of legendary Australian photographer Max Dupain, you can see a world with different details but the essence of the subjects is the same.

A 1940s Dupain photo taking in the sweep of Bondi shows rows of parked cars, that beautiful pavilion and the crowds of people clumped around the flags.

Another shot from the time shows a bloke, hands on hips, surveying the surf while his female companion picks at the hem of her swimsuit.

Aside from the fashions and the shapes of the cars, it could be today.

So much of the way Aussies — and especially Sydneysiders — see themselves is wrapped up in the beach.

From a cultural point of view, there are Dupain’s photos, Charles Meere’s 1940 painting Australian Beach Pattern, full of robust beachgoers, and even Kathy Lette’s visions of 1970s “Neanderthal” surfers and the girlfriends who watched them from the beach.

FOR MORE PICTURES BY PAUL BLACKMORE GO TO INSTAGRAM @PAULBLACKMOREPHOTO

But it’s even more ingrained than that. It’s the shared experience of those tiny moments of a Sydney summer that we all know so well.

Trying to wolf down a soft-serve ice cream before it becomes a puddle on your clenched fist.

The tang of vinegar rising from hot chips at the next picnic table. The scalding sand burning your toes as you dash, thongs in hand, to find somewhere to set up camp for the day.

The thrill of diving through that first wave or the mild panic when you misjudge it and get dumped.

It’s that shared experience that makes Aussie beach culture unique, according to ocean swimmer Paul Ellercamp.

The founder of oceanswims.com says it’s a lifestyle that starts early, especially for those lucky enough to live near one of the beaches.

“When I was a kid we lived only a couple of hundred metres from our beach and it was like another room of the house,” he says.

“Australians think of the beach as being part of their life, part of their lifestyle, and being in the surf becomes second nature. In that way, we’re probably different to a lot of other nations.

“I mean there are some strong beach cultures around the world. But I think it’s unusual to find one that’s mixed up with that easygoing assumed experience of having the beach so readily available and having it as a normal part of your life.”

Ellercamp has seen that shared experience broaden in recent years with an explosion in open water swimming.

Last summer, more than 50,000 swimmers participated in almost 900 race swims monitored by his website.

It’s evident in the informal swim groups that have popped up around the city (and the country).

And it can also be seen on any given day in the number of lone swimmers doing laps at Bondi — from Icebergs to the boat ramp and back again.

Part of the appeal, Ellercamp reckons, is the chance to explore an environment just beyond our own. “It’s one of the good things about ocean swimming — that you can be a pioneer, if you like,” he says.

“You’re sort of on the edge of civilisation but you’re actually still close to home and still close to a cuppa.”

A favourite city beach for Ellercamp is Coogee, especially on a day when the swell isn’t too high and you can swim around Wedding Cake Island at close quarters.

“If you go really close to it, you get to see the bottom much more clearly,” he says.

“There are big boulders down there, rolled smooth by hundreds of millennia of years’ wave action.”

And for those of us not quite ready to head for the open water, there are always the ocean pools dotted around the city beaches. There’s Coogee’s trio of well-known sites — Wylie’s, McIver’s and the bogey hole — or Clovelly’s Geoff James Pool.

For Blackmore, however, his favourite is the most special of them all.

“I swim a lot at the Icebergs and that’s just one of the greatest spots on Earth,” he says. “We’re just very lucky to have that.”