Ysgol Gyfun Cwm Rhymni is a Welsh-medium school situated in the village of Fleur-de-Lys in the Rhymney Valley.

The previous school is now called Ysgol Gyfun Cwm Rhymni – Safle Gellihaf so it is not confused with the other campus.

[3] Ysgol Gyfun Cwm Rhymni has a strong reputation in relation to sports, especially in rugby and athletics.

Cwm Rhymni has a very large catchment area stretching from Rhymney near the top of the valley to Caerphilly.

Prior to the establishment of Ysgol Gyfun Gwynllyw in 1988, Cwm Rhymni's catchment area also included the whole of the county of Gwent and pupils attended the school from as far afield as Newport and Chepstow.