Wandering the narrow medieval streets of Bilbao's Casco Viejo, you'll stumble upon the towering exterior walls of Santiago Cathedral. It is believed that the church, which serves as a stop for pilgrims trekking the northern Camino de Santiago (Way of St. James), dates back over 600 years, when it was built on the site of two previous even older churches.
Today's cathedral – which shouldn't be confused with the much larger one of the same name located in Santiago de Compostela, at the end of the Camino de Santiago – has expanded over the course of time, growing to the cathedral that you see now. During a visit, you can peruse its many chapels, wander the peaceful 15th-century gothic-style cloister, or just take in the exterior with its 19th-century gothic-revival facade and spire.
Santiago Cathedral is located amidst the original seven streets of Bilbao's Casco Viejo (old quarter). While the interior is quite humble compared to many of its other European cathedral counterparts, it serves as a tranquil respite from the busy medieval barrio, and of course provides a unique look into Bilbao's past.
You will find the Santiago Cathedral located in Plaza de Santiago, where it can be visited for a cost of three euros. Note that it is closed on Mondays, and open Tuesday through Saturday from 10am to 1:30pm and then again from 4pm to 7pm. You can also attend mass on Sundays at either 10:30am or 1:30pm.