The castle was actually a restaurant

Castell dels Tres Dragons sounds older than its job description. Lluís Domènech i Montaner designed it as a café-restaurant for the 1888 Universal Exposition, an ambitious permanent building meant to represent contemporary architecture and craft. Later it became deeply associated with Barcelona's natural-science collections and remains part of the Museu de Ciències Naturals' scientific infrastructure. That sequence matters: leisure spectacle became museum science. Look at the exposed brick, towers and fortress-like silhouette, then keep the date in mind. This is not a medieval castle surviving inside the park. It is a late nineteenth-century exhibition building deliberately playing with historical architectural language while using modern materials and ambitions.