Permeability and openness are key features of the Groot Klimmendaal Rehabilitation Centre in Arnhem, a small town in eastern Holland. The building blends effortlessly with the surrounding forest, the filtered forest light permeating the building. The healthcare centre is open on another level too, being designed for use not just by patients but also by the local community. In fact it is part of a broader masterplan by architect Koen van Velsen to turn the area into a public park with three high-density buildings. The building merges into its forest setting thanks to its minimal footprint, slender stilts supporting the upper cantilevered levels, an almost fully glazed double-height ground floor, the bronze-coloured anodised aluminium cladding on the upper levels that help camouflage and dissolve this 14 000 square metre volume in the forest. The spatial distribution programme is immediately readable: offices below, healthcare services above, and the Ronald McDonald House on the roof. Transparency and permeability blend and dissolve interiors with the exterior, the double-height first floor glazing ensuring the least conspicuous of partitions. The glazed bow windows of the restaurant seem to bring the forest right into the room. From the inside, the full views and filtered light are an explicit invitation to occupants to make contact with nature, a key element of patient rehabilitation. For the healthcare concept underpinning the whole project is that a positive, stimulating environment contributes to patient wellbeing and successful rehabilitation. Hence the programme to make the centre a social meeting place for the wider community, open to all not just patients. The double-height ground floor also hosts the sports and fitness areas, a restaurant and theatre, all of which may are used by patients, their family and the general public. In this way both the healthcare centre and its patients are an integral part of the local community. The feeling of security and wellbeing that pervades the Groot Klimmendaal Centre is also the result of close collaboration between architect Koen van Velsen and end users, who had a say in things like vertical distribution, colour schemes and materials. A gently graded staircase runs the length of the whole building, connecting the different levels physically and visually. As well as providing a clear perception of how the internal spaces unfold, it also stimulates and facilitates physical exercise. The whole programme was conceived around the concepts of sustainability, ease of maintenance and flexibility. As a compact volume it needs less energy - supplied by energy-efficient mechanical and electrical plant. A system of thermal storage further helps reduce energy requirements. Sustainable building materials were employed; the flooring was chosen with low maintenance in mind; ceilings and façade cladding are also low-maintenance and long lasting. Although built to serve particular end-user needs, the programme has been designed to allow for future spatial distribution changes as required. This feature, the transparent design and social integration, make the Groot Klimmendaal an exemplary healthcare architecture.