Sited just below the crest of the mountain at Penrhys stands the small nondescript stone 'hut-like' structure known as Mary's well.

This unassuming building houses the spring that has been the focus of religious life at Penrhys, dating back to the earliest days of Christianity in the Rhondda.

This spring has throughout its recorded history been attributed with miraculous healing powers said to be of divine origins. Research suggests that the spring's focus as a place of worship and healing, actually pre-dates Christianity, and is actually of pagan origin.

In common with many springs of this nature pagans believed it to be a dwelling place of divinities and thus possessing mystical powers. Christian missionaries on discovering such superstitions attached to a spring such as this at Penrhys, would endeavour to subvert these traditions, placing the responsibility for the 'miraculous powers' associated with them as being of Christian origin.

Thus the spring at Penrhys became dedicated to Mary, and the healing attributes became a gift from God to the righteous.

The spring was said to be effacious in curing many ailments, such as 'rheumatism, king's evil' and particularly eye disorders. In addition the spring waters for many years were used in baptisms at the local parish church. Penrhys was what is known colloquially as a 'pin well' as the person hoping to be healed would, after taking the waters, cast a pin into the well. If the pin became discoloured it was a sign that their petition would be granted. It is said that even in the twentieth century 'scores of pins' were often to be found lying in the well.