The Bükk National Park is a national park in the Bükk Mountains of Northern Hungary, near Miskolc. It was founded in 1976 as the third national park in the country. It contains 431.3 km² (of which 37.74 km² is under increased protection). Mountainous and forested, Bükk is Hungary's largest national park and is situated in the northern mountains, between Szilvásvárad and Lillafüred. Bükk's important geological features include various karst formations within its limestone mountains - particularly caves (once inhabited by pre-historic people), swallow-holes, and ravines. The country's longest (4,000 metres) and deepest (245 metres) cave, Istvánlápa, is located in the park. Bükk National Park also contains ninety species of nesting birds, some considered endangered.