I’d only been to Hamburg once before: in the depths of winter, when hunkering down in a dingy St Pauli bar was the main aim of the trip. But Hamburg in summer is a different story.

On a sweltering day in August, I hired a bike and went west, out of the city centre, along the River Elbe. I had been told there were urban beaches along the river and I was keen to take a look.

Away from the city’s hustle, I stopped to admire a cheerful-looking red lighthouse at the water’s edge. A terrace of cafes and restaurants looked over the river, with waiters rushing to and fro with large trays of beer and snacks for their many customers. Over the other side I could see a long stretch of sand, teeming with sunseekers.

A narrow path led behind the restaurants, parallel to the beach. On my right were dainty, picture-perfect wooden houses, with roses around the door and parasols peeking jauntily from windows. Gardens belonging to the houses were on the other side of the path to my left, with families playing on the grass and elderly couples sipping cool drinks in the shade.

Beyond the gardens was a beach scene like no other. A strip of sand, maybe 50 metres wide, was packed with people sunbathing, building sandcastles, playing beach games and generally doing what people do on beaches. It seemed like all of Hamburg was on the beach that day. But what made it extraordinary was the backdrop. Immense container ships cruised past, causing waves to crash on the shore for excited young children to jump over. And on the far side of the river stood colossal industrial cranes, like giant metal beasts, surveying the sun-drenched spectacle.

I walked a little further, past the Ahoi Strandkiosk, and found a spare metre of sand to myself. A group of friends were enthusiastically playing volleyball in the water in front of me. I took a crafty shot, thinking they might not appreciate having their photo taken. But it soon became apparent that no one on this gorgeous summer’s day gave a hoot about some woman taking photos on a crowded beach. I snapped away at everything and everyone. This scene is a favourite because of the moment of carefree happiness captured between friends, against the backdrop of the city’s harbour giants – those majestic metal cranes.

• Celia Topping is a photographer and journalist based in Berlin and London