The Basilica of Santiago de Compostela
The Catedral de Santiago de Compostela sits at the end of the Camino de Santiago (The Way of St. James), one of the three main pilgrimage routes of medieval times (more on that here).
Inside is the world's largest botafumeiro (second image below), a huge incense burner that swings above the heads of pilgrims. Cynics like to say it mitigates the odors given off by sweaty pilgrims massed inside the basilica.