The Fontaine de la Vierge is a spring behind the church in the centre of Rostenen. It has been a place of pilgrimage for at least 700 years, which is reflected by the stonework around the water - some of it is obviously very old, and some of it more recent. Today, it is a very attractive spot, just far enough removed from the hustle and bustle of the town to offer a moment of rest and tranquility. It is always kept clean and tidy, and although it is an outdoor, open site, visitors are respectfull, probably mindful of the ancient traditions associated with the spot.

The modern history of the spring can be dated back to around 1300, when locals noticed a rose bush that seemed to remain in bloom almost all year round. According to the story, they decided to investige the ground in which the rose bush was growing in search of an explanation of its behaviour, and they came across a wooden statue that had clearly been in the ground for some time, but was unmarked. A spring bubbled up around the statue, and it was not long before the spring was found to have healing properties. The statue was of a woman, and was said to be of the Virgin Mary. It seems possible that the statue was either of Roman origin or dated back to the time of the Breton Saints, signifying that the site has had religious significance for a very long time.

The phenomenon ot the statue and of the healing well became very well known during the Middle Ages, and pilgrims started to come far and wide to visit Rostrenen. A town built up around the well and a church was built to house the statue. Although Rostenen was never an important administrative centre for the Breton Church, it was an important centre for pilgrims, which explains why the town has such a large church and why the building is designated as a Collégiale rather than as a simple parish church.

Although not as famous as in former times, the Fontaine de la Vierge still receives visitors hoping to find a cure for their ailments.