The Tossa de Montbui Castle is located at 620 m above sea level on a hill in the southwestern sector of the city of Igualada. Since medieval times, it has occupied a strategic position for territorial defence and the control of surrounding fortifications, and it was first documented in the year 960.
The castle is defined by a rectangular plan, measuring 9.50 m in width and 14.50 m in length, organised along a north–south axis. Its perimeter walls, approximately 2 m thick, are built in locally sourced calcareous stone with lime mortar joints and are characterised by rounded corners.
A central objective of the project was to enable access to the upper levels of the tower while preserving the legibility of the existing ruin. This was addressed through a strategy informed by historical studies that identified the presence of a former slab roof above the first floor, together with typological comparisons with similar medieval towers.
The intervention is based on these readings, and the reinforcement of the existing masonry is carried out alongside the introduction of new architectural elements derived from historical references. These additions allow access to the uppermost level of the tower, which is reactivated as a viewpoint over the surrounding landscape and the network of frontier castles, without compromising the integrity of the original structure.
A second key concern was the balance between contemporary construction and historical authenticity. This is addressed through a deliberate differentiation of new and existing material, allowing the intervention to remain legible while reinforcing the ruin.
The ascent to the upper level is resolved through a staircase that reconstructs the western wall and reinterprets the original wall-carved stair typology, typical of towers of this period. Its steep geometry is maintained in order to preserve the sense of incompletion and the perception of the ruin as an open historical condition.
In continuity with this approach, a partial slab is introduced at the level of the main floor, forming a small north-facing balcony. This element is understood as a reactivation of a possible original exterior access, re-establishing a direct relationship between the tower’s interior and the surrounding landscape.
Overall, the project demonstrates how minimal but precise interventions, grounded in historical analysis, can re-establish spatial continuity and accessibility while maintaining the autonomy and readability of the existing architectural remains. 
