This reserve, set in the magnificent Massif de la Boine, contains Ardennes forest fauna (deer, stags, boars) and, in a vast clearing, animals that once lived in the area: bison, brown bears, ibex, chamois, wolves, tarpans (small horses), wild oxen (an extinct species recreated by cross breeding) and Przewalski horses, which originated from the Russian steppe. The Lesse disappears beneath a rocky arch at the Gouffre de Belvaux chasm, then reappears at the Trou de Han.