Following the trend towards open data, various cultural organisations offer information about their collections. However, these knowledge bases are not used to accompany a visit to historical monuments. We think that a possible explanation for this observation lies in the distinction between availability and accessibility of the knowledge offered: although these knowledge bases make this knowledge available, it is difficult for non-experts to make use of it and make it their own. Rather than a semantic approach to visiting based on description, we advocate an active and semiotic approach based on comparison. We have identi- fied four challenges in applying this approach to church stained-glass windows. The first two challenges are to link the physical space of the building and the stained glass with the documentary space so that visitors can move between the two. Visitors also need to understand and use 'reading keys' to match a represen- tation with its subject. Visitors should afterward finally be able to use their knowledge and skills on other visits. Through interviews and observations, we have iteratively designed paper and digital prototypes to meet these challenges.