Most forests in Europe today are 'managed' - the trees are planted in tidy rows and cut down every few decades. Białowieża is different. The trees fall when they're ready, the moss creeps over the logs, and new trees grow up in the gaps. It is what most of Europe looked like thousands of years ago.
Walking through Białowieża feels like stepping into a fairy tale. Some oaks are so wide that it takes five children holding hands to circle the trunk. The forest floor is soft and springy with hundreds of years of fallen leaves. Woodpeckers drum on the dead wood, and in winter the snow muffles every sound.
The most famous animal here is the European bison, called żubr (pronounced 'zhoobr') in Polish. They are huge - a male can weigh almost a tonne, about the same as a small car. A hundred years ago they had almost disappeared from the wild. Polish foresters and scientists slowly brought them back, and today around 800 bison live free in Białowieża.
Other animals share the forest too: wolves, lynx, beavers, moose and deer. Because nobody has cut the forest down, lots of rare insects, mushrooms and plants live here that you cannot find anywhere else on the continent.