The Chapel of St. Gangolphe is located in a wonderful location near the northern limit of Schweighouse and at the entrance of the valley that leads to the col of Bannstein. The small shrine contains frescoes dating from the time of Martin Schongauer and chronicling the life of the saint. He was honoured as the patron saint of sources and as guardian of marital harmony. According to the legend, Gangolphe was a noble knight of the Merovingian palace of Burgundy under Pepin of Herstal in the 8th century. After returning from a war campaign, he discovered his wife's committing adultery with a priest. Although maintained in the water of the fountain, the woman's arm was burned; this phenomenon allowed divine justice to prove the guilt of the wife. Gangolph would then have left the scene and withdrew himself at Avalon in religious peace. But he was killed through a sword thrust by the woman's lover on 11 May 760. Various miracles occurred at his tomb in Varennes and he was canonized at the end of the 9th century. His feast is celebrated at Schweighouse the first or second Sunday of May with a religious ceremony and a little "cuckoo market".