A small group of enthusiasts has embarked on an unusual project to build a fortress using techniques from the Middle Ages. This effort is part of a unique architectural challenge that was launched nearly 19 years ago. The project, known as Guédelon Castle, is guided by the motto "Build to understand." It aims to reconstruct historical architecture through hands-on construction, allowing participants to gain a deeper insight into the methods and materials used during the medieval period. Located in the village of Chailly-sur-Aube in northeastern France, Guédelon Castle is being built without the use of modern tools or materials. Instead, builders rely on traditional techniques such as stone masonry, timber framing, and manual labor. The goal is not only to create a visually accurate replica of a medieval fortress but also to study and preserve the knowledge of historical construction practices. The project has become a living museum of sorts, attracting visitors who can observe the construction process and learn about the challenges of building without modern technology. Experts and volunteers work side by side, using period-appropriate tools and methods. This approach allows for a more authentic reconstruction and provides valuable educational opportunities for those interested in history and architecture. Guédelon Castle is expected to be fully completed in the coming years. Once finished, it will serve as both a historical monument and a research site, offering insights into the engineering and craftsmanship of the medieval era. The project stands as a testament to the enduring fascination with the past and the value of hands-on learning in understanding historical practices.