The city of Madrid, founded on a complex underground network of canals, finds in its waterways one of the most silent (yet fundamental) infrastructures in its urban history. This system of pipelines, active from medieval times until the mid-19th century, not only guaranteed the water supply to the population, but also enabled the construction of an urban landscape articulated by numerous squares, parks, and gardens in which water always played a central role, through elements such as canals, ponds, and fountains.

In this sense, a case of particular interest (if not, the most) is the area surrounding the Paseo del Prado and the Royal Site of Buen Retiro, now recognized as a World Heritage Site by UNESCO. This urban fragment underwent numerous transformations from its origins as a place of productive retreat to its consolidation as Madrid’s main urban scene, accumulating a large number of historical layers. Of all these layers, the deepest is, precisely, the water system that flowed underground, silently, connecting its main avenues, gardens, and buildings to enable both beauty and functionality.

In this transformation process, the figure of the architect Juan de Villanueva would play a very significant role: while his architectural legacy has been widely recognized and studied from a purely monumental perspective, his participation in the planning and improvement of Madrid’s hydraulic infrastructure has received little attention. The truth is that, beginning in 1783, the architect assumed the inspection and renovation of the waterways around the Retiro Park, a responsibility that he carried out in parallel with the construction of his three major scientific projects for the Salón del Prado: the Royal Botanical Garden, the Cabinet of Natural History, and the Royal Astronomical Observatory. In this way, our current Paseo del Prado is the result of a comprehensive intervention between architecture and engineering that, far from acting autonomously, came together through a single urban project to achieve the materialization of a highly ambitious but no less complex idea.

Villanueva’s intervention in the layout of these waterways and in their collection, conveyance, and distribution systems, as well as their connection with the urban complexity of 18th-century Madrid, also demonstrate the existence and mastery of a sophisticated hydraulic culture and infrastructure, revealing a much less iconic but equally decisive facet of his work and, above all, of his impact on the city.

Today, Villanueva’s hydraulic legacy in the city of Madrid remains largely hidden, deteriorated, or in disuse. However, beyond the vindication of the historical interest of the underground structures that make up the waterway network, it is possible to engage in a contemporary reflection on its valorization through heritage recognition and reuse. Thus, in the face of the progressive deterioration of the system, confirmed by multiple recent technical reports, the possibility of its partial recovery as an educational urban resource, as a landscape element, or even as a sustainable strategy for water management arises. At this intersection of memory, technique, and design, waterway journeys occupy an indispensable place, on the one hand, in Villanueva’s work; and, above all, in the construction of Madrid’s urban identity.