Galway was one of the most important Atlantic ports of north-western Europe during the Middle Ages, and it was natural that its main church should be dedicated to St. Nicholas of Myra who, although better known to us today as Santa Claus, was also the patron saint of mariners. The church was founded in 1320, and remains one of the best-preserved and best-kept of Ireland's medieval town churches, but it is unique among them in having a triple nave. The carvings on the exterior windows are worthy of inspection, showing foliage, a dragon and even a mermaid, an appropriate maritime theme.

Equally engaging are the gargoyles of the tower which has a carillon of bells ranging in date from the sixteenth to the nineteenth century. Any medieval church furnishings of value were misappropriated by the English king's Lord Deputy Leonard when he came to Galway in 1537 to ensure that the loyal inhabitants of the town turned their religious allegiance from the Pope to king Henry VIII. Cromwellian troops cleared out anything that may have been left, though fragments of two wooden mitres and a crown managed to survive.

Interior medieval highlights are of necessity, therefore, of stone, notably the carvings of the arches leading from the outer naves to the transepts, where angels, foliage and heraldic merchants' marks may be found. Further fine stonework of fifteenth / sixteenth-century date is found in the south transept.

Local legend states that Christopher Columbus worshipped there when he visited the city in 1477. It is the largest medieval parish church in Ireland in continuous use as a place of worship.