The château de Selles (dating back to the 14th century) in Cambrai is one of the most important monuments in France for medieval graffiti. Today the some parts of the engraved walls are endangered by a complicated weathering process. The present project lead by archaeologists in collaboration with universities and companies which are specialized in 3D surface scanning and 3D modelling aims to apply archaeological methods and new optic technologies in order to preserve the endangered engravings and to study the graffiti. For documentation, color photography (fontal and side light) is used for the survey, archive and deciphering by tracings of the engravings. 3D high resolution scanning of the engraved parts of the walls have been used to get a digital print of most of the traces on the wall in order to be able to work on the 3D models. The 3D models of the engraved are used by archaeologists and paleographers to explore precisely the engravings and decipher objectively the motif and texts. The repeated 3D scanning of some parts of the castle have led to a 6 year monitoring of the weathering processes. A complete photogrammetric survey was made on the outside and inside of the castle in order to build up a virtual visit to the castle thanks to a virtual reality headset that helps the visitor to discover the engravings in an immersive experience.