Structural change is an abstract term. When old industrial sites are put to new uses, surprising moments arise. Zollverein coal mine is one such example. The 100-hectare site with 96 buildings, over 200 technical installations and machines, around three kilometres of conveyor bridges and over 13 kilometres of pipelines is one of the world's largest industrial monuments. Embedded in its centre – somewhat hidden – is an open-air swimming pool. Measuring 60 square metres, this pool may not score points for its size, but it makes people happy all the more.

Rust red and light green, the unique backdrop of the former coking plant rises to dizzying heights, whilst azure blue sparkles in it the calm water surface of the works swimming pool – it sparkles even when the sky is grey. The summer at Zollverein has not stayed dry for years. Wooden planks frame the pool and on the shady side a puddle traces the contours of an elephant's back. Every year during the summer holidays, everybody finds the perfect way to cool off here: free of charge, as there is no entrance fee. The fact that the bathing fun is free for everyone, however, not only pleases school children and swimmers from the region, but also the tourists. They come from neighbouring towns and cities and from far away.

The swimming instructor has been working as a lifeguard at the works swimming pool for 12 years whenever North Rhine-Westphalia takes its summer holidays. Every year she enjoys coming back to work here, which is mainly due to the clientele. "We really do have a lot of nice visitors," she says while standing in the shade next to the stairs leading up to the pool. On hot summer days like this, the whole world meets at the works swimming pool. The Ruhr Valley goes swimming.