Specialty coffee in Olsztyn: 5 checked cafés

The first lake in the world that people deliberately cured lies in Olsztyn, on the university campus. In the winter of 1956, Professor Przemysław Olszewski sank a pipe into Lake Kortowskie, nailed together from planks and covered in tar paper — a hundred and eighty meters long, the intake thirteen meters below the surface — to siphon the dead water off the bottom. The water cleared, the algae thinned out, and the Kortowo method was later repeated on more than a dozen lakes in Europe and North America. Fiberglass replaced the wood in the 1970s, the pipe is still working, and the lake is clean because it sends its worst water downstream.