This fortified church was built to defend the village of San Nicolas. Today there's only one watchtower remaining of the original three, and the entire perimeter of the church is surrounded by fortified porches. In the corner you can see a representation of St Nicolas' seal in stone. The floor is made of oak, and there are several numbered graves set into it, with coats of arms belonging to noble families. There's a beautiful crucifixion and a carving of St Nicolas on the old altarpiece. The large Baroque organ is one of the most important in Pamplona. Entrance is free.