Grotte di Castellar de n'Hug

Castellar de n'Hug, a municipality in the Berguedà, contains 14 inventoried cavities: 10 caves and 4 pits. Together they total 910 m of passage and reach a maximum depth of 25 m. All the recorded cavities develop in limestone.

The Surgència de Rus is the longest and deepest cavity in the municipality, with 555 m of passage and 25 m of depth; it is an active spring with six sumps passed and 215 m completely flooded. Other notable cavities are la Tuta, 83 m, known since time immemorial and explored and surveyed on 19 July 1959 by the GIE; the Cova de Rus, with 6 entrances and 63 m of passage on the southern slope of the tossal de Rus, within the Cadí-Moixeró natural park; the Forat Nº1 del Tarter, a pit 19 m deep at the summit of Pla Baguet, explored and surveyed in 1978 by the GE Badalona; and the Forat del Clot dels Torrents, a pit 15 m deep on the torrent de la Font del Boix, of imprecise location.