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.
The text describes Istvánlápa, a significant cave in the Bükk National Park, highlighting its length and depth. It also mentions that the park is home to a diverse range of bird species, including those facing endangerment.