Many historical European cities are home to houses of great heritage value. These structures have been able to provide comfort throughout history without the use of artificial conditioning systems. Even though such dwellings were influenced by academic styles, by contradicting vernacular architecture, their adaptation to local climate in order to achieve thermal comfort is commonplace. They were mostly built within compact urban tissues, making use of local materials, workforce and construction technologies. Learning from the past knowledge of these design strategies that are specifically adapted to specific climates can play a significant role in reducing the energy demand of extant buildings. Likewise, this paper thoroughly investigates the remaining urban conglomerate of Cadiz from a scientific approach. An original simulation software, duly tested with on-site measurements, was used to analyse the passive design strategies that were applied effectively. The results of this study indicate that historic neighbourhoods in Cadiz are creatively adapted to their natural conditions. In this sense, the main conclusion is that in mild climates, the combination of a compact urban tissue and climate responsive dwelling design should be sufficient to maintain acceptable indoor comfort levels.