In the north-east of Campania Felix, separated from the Campania Apennines by the valley of the Medio Volturno, the massif of the Trebulani Mountains rises, also known as the Colli Caprensi.

The longest river of Southern Italy with its 175 kilometres rises in Molise, at Rocchetta a Volturno and runs for a long way in the Apennine region, of which, after the Ponte 25 archi, marks the border with Campania.

With a surface of just over a square kilometer, the enchanting Lake of Letino was created at the beginning of the twentieth century in order to feed the hydroelectric power station of Prata Sannita.