The pilgrimage church of the Assumption of the Virgin Mary, now called the Unterkirche by the people of Hallenberg, dates back to the 11th century and was once the parish church of the defunct village of Merklinghausen. It is therefore the cradle of the town of Hallenberg.
It houses the miraculous image of 'Our Lady of Merklinghausen', which attracts numerous pilgrims to Hallenberg every year in August on the Solemnity of the Assumption.