The Białowieża Forest (Puszcza Białowieska) is thought to be the last remaining intact primeval forest in Europe. The forest is home to around 800 wisent (żubr in Polish), which is a protected species of European bison. You can watch them in their natural environment.
The European bison (Bison bonasus), or 'wisent', is similar in appearance to its North American relative. Bison in the Bialowieza Forest in Poland have traditionally been fed hay in the winter for centuries, and vast herds may gather around this diet supplement.