Nant-y-Ffrith refers to a stream and the wooded valley through which it flows on the border between Flintshire and Wrexham County Borough in Wales. The stream begins in moorland to the east of Llandegla. It passes Bwlchgwyn village before entering a rather steep-sided, rocky valley. It passes under the viaduct of a disused railway line before joining the River Cegidog at Ffrith. The woodlands contain some deciduous trees but are dominated by recent conifer plantations planted by the Forestry Commission after the second world war. They contain a range of flora and fauna including various ferns and mosses and woodland birds such as wood warbler and redstart. During the 1950s, people travelled from miles around to park their cars on the Drofa (or hair-pin bend in English) overlooking Nant-y-Ffrith, and listen to nightingales, whose song echoed in the valley. There are several abandoned silica quarries and lead mines in the area. Lead mining may have begun as early as Roman times and has left a number of caves. The mountain on the Flintshire side of Nant-y-Ffrith in modern Welsh is called the Penllyn. Pen in Welsh literally means 'head' and is often used to describe a notable high point, a pinnacle. The name has its origins in ancient history. The Brythonic precursor to modern day Welsh used the word across Britain's landscape: 'Penmaenmawr', 'Penmachno' and the 'Pennines' in the Lake District. The ancient Welsh using the word to describe the mountain ties with evidence of roundhouse foundations discovered on the Penllyn sometime during the 1960-70s. There are also other pointers to ancient Welsh history on the mountain in its name. On older maps there are variations of a full name, 'Pen llun y gwr' and 'Pen llan y gwr'. The word 'gwr' at the end is interesting, meaning 'man' maybe an elder or leader in this context. 'Gwr' also appears in the nearby village of Caergwrle. The inclusion of 'gwr' in the hillfort's name may have provided a differentiation for the ancient Welsh with other nearby hillforts, Pen llan y gwr perhaps having been a seat of tribal governance or set up by an older generation.