The Castle of Isola del Liri rises on a travertine rock that blocks the course of the Liri river, forcing it to split into two branches and form the famous waterfalls, the better known Cascata Verticale (Vertical Waterfall) to the south and the no less impressive Cascata del Valcatoio or Cascatelle (Waterfalls) to the west; both are 27 metres high and have the peculiarity of being the only ones in the world to fall into a built-up area.