Bilbao's Casco Viejo was founded in 1300 on a flood-prone bend of the Nervión, its original seven parallel streets—the Siete Calles—still form the district's spine six centuries later. Somera, Artecalle, Tendería, Belosticalle, Carnicería Vieja, Barrencalle, and Barrencalle Barrena run east to west, linked by narrow alleys that once channeled rainwater to the river. The Gothic Catedral de Santiago anchors the northern edge, its spire visible from every approach, while the neoclassical Teatro Arriaga marks the southern boundary where the old town meets the Ensanche expansion. The district survived French occupation in 1808, liberal uprisings in the 1830s, and Carlist sieges that left scorch marks still visible on the Church of San Antón's façade. By the mid-twentieth century, industrial decline had hollowed the quarter—stone buildings stood empty, commerce moved to modern Bilbao, and demolition seemed inevitable. Preservation efforts began in the 1980s, converting crumbling merchant houses into cultural spaces while retaining façades, balconies, and the cobblestone grid. Plaza Nueva's arcaded perimeter, completed in 1851, now hosts Sunday stamp markets and pintxo bars where txakoli flows from shoulder-height spouts. Architectural layers accumulate vertically: Roman foundations support medieval load-bearing walls, nineteenth-century ironwork adorns Baroque doorways, and twentieth-century shopfronts occupy ground floors of fourteenth-century structures. The Ribera Market, Europe's largest covered market when it opened in 1929, spans 10,000 square meters under Art Deco stained glass, its vendors still selling line-caught hake and Idiazábal cheese wheels. Narrow passages like the Calle de la Cruz connect major arteries, their overhead galleries—pasadizos—allowing residents to cross between buildings without descending to street level, a vestige of defensive architecture adapted for convenience. Today the Casco Viejo functions as both living neighborhood and historical document. Residents hang laundry from wrought-iron balconies, schoolchildren cross the Zubizuri footbridge to class, and guided walking routes trace the medieval street plan. The district remains accessible around the clock—its plazas, churches, and lanes open to pedestrians year-round—while organized bilbao old town guided walk experiences provide historical context that static plaques cannot. Restoration work continues: the Church of Santos Juanes, damaged in the 1983 floods, reopened in 2014 with its fifteenth-century retablo intact, and the Euskal Museoa chronicles Basque maritime and industrial history in a sixteenth-century cloister. The quarter's density—thirty blocks containing fourteen churches, three markets, and two hundred bars—rewards repeat visits, each pass revealing details missed before.