Lorraine Williamson
Spain’s rich history is well documented, but beneath its cities and landscapes lies a lesser-known world. Ancient tunnels, sunken villages, and cave dwellings reveal stories of resilience, war, and adaptation. While most visitors focus on Spain’s grand landmarks, below their feet are remnants of civilisations that shaped the country’s past.
From Toledo’s secret tunnels to the flooded village of Sau, these subterranean sites offer a glimpse into a forgotten world. Each location tells a story, offering insight into Spain’s complex cultural and historical evolution.
Toledo’s underground labyrinth
Toledo is renowned as the city of three cultures, where Christians, Jews, and Muslims once coexisted. Beneath its streets lies an intricate network of tunnels, many dating back to Moorish rule. These passages served as escape routes, military defences, and later, hiding places during the Spanish Inquisition.
One of the most significant discoveries is the Termas Romanas de Toledo, an extensive Roman bath complex spanning 3,000 square metres. Also buried beneath the city are the Baños Islámicos y Judíos, ancient bathing sites that highlight Toledo’s diverse heritage. Myths even suggest that Hercules built a secret underground palace here. While no such treasure has been found, the Cueva de Hércules remains a mysterious site, likely a former Roman reservoir.
Today, guided tours offer access to sections of these hidden passageways, providing a rare look into Toledo’s layered history.
Seville’s Cathedral and its Islamic roots
Seville’s Gothic cathedral is one of the largest in the world, but its foundations tell a different story. Before its construction, the Mezquita Aljama de Sevilla stood on the same site as the city’s main mosque. After the Christian reconquest in 1248, the mosque briefly served as a cathedral before an earthquake in 1356 led to its replacement.
However, remnants of the original structure remain. The Giralda, originally a minaret, now functions as a bell tower. The Patio de los Naranjos, once a mosque courtyard, provides a shaded retreat. The Puerta del Perdón, with its horseshoe arches, preserves traces of Islamic design.
These architectural elements serve as reminders of Seville’s layered history, where Islamic and Christian influences intertwine.
The cave dwellings of Guadix
In Granada’s Guadix region, thousands of families still live in casas-cueva, traditional cave dwellings carved into the soft rock. Dating back to the Moorish era, these homes provided refuge following the Christian reconquest.
Far from primitive, these cave houses offer natural insulation, staying cool in summer and warm in winter. Many now include modern amenities such as running water, electricity, and WiFi. Visitors can experience this unique way of life by staying in a cave hotel or exploring the Cueva Museo, which showcases the region’s history.
The sunken villages of Franco’s Spain
In Catalonia, the Pantà de Sau reservoir hides the remains of a lost village. Flooded in the 1960s to create a water supply, the village was abandoned and submerged. The church of Sant Romà de Sau is usually the only visible remnant, its bell tower rising above the surface. However, prolonged droughts have drastically lowered water levels, revealing entire streets and buildings.
The flooding of villages was a common practice during Franco’s dictatorship as part of efforts to modernise Spain’s infrastructure. Dozens of rural communities were displaced to make way for reservoirs, often with little consultation or support. Many villagers were relocated to newly built settlements, though these were frequently poorly planned and lacked essential services. Others moved to cities in search of work, contributing to the depopulation of rural Spain.
In early 2025, the reservoir dropped to just 7% capacity, fully exposing the village. After recent rainfall, water levels rose to 31%, partially submerging the ruins again. This fluctuating landscape serves as both a historic site and a stark reminder of Spain’s changing climate.
Franco’s forgotten bunkers
During the Spanish Civil War and Franco’s dictatorship, Spain was fortified with defensive structures. One of the most significant was the Línea P, a network of 6,000 bunkers constructed between 1944 and 1948 to defend against a feared French invasion.
Although never used in combat, many bunkers remain intact. In the Valle de Canfranc, visitors can explore Punto de Apoyo No. 1, a site that once guarded the International Train Station of Canfranc. Hiking trails now pass through this forgotten military network, offering a rare insight into Spain’s wartime history.
Uncovering Spain’s underground legacy
Spain’s subterranean world offers an alternative perspective on its history. From the secret tunnels of Toledo and the hidden mosque beneath Seville’s cathedral to the sunken village of Sau and the wartime bunkers of Franco’s regime, each site reveals a different aspect of the past.
Many of these underground sites are accessible through guided tours, providing an opportunity to explore a side of Spain often overlooked. For those seeking to go beyond the usual tourist spots, the country’s hidden depths offer a fascinating journey through time.