The pilgrimage church of the Assumption of the Virgin Mary, which today is called Unterkirche by the people of Hallenberg, dates back to the 11th century and was once the parish church of the vanished village of Merklinghausen. It is therefore the cradle of the town of Hallenberg.
It contains the image of Our Lady of Merklinghausen, which every year in August on the feast of the Assumption of the Virgin Mary leads numerous pilgrims to Hallenberg for pilgrimage.