Monitoring of cultural heritage structures is an application area for Wireless Sensor Networks (WSNs) which is implemented in the project "Smart Monitoring of Historic Structures (SMooHS)", funded by the European Commission within the 7th Framework Programme. The project aims at the development of a WSN system especially designed for use on real structures to enable smart interpretation of acquired data and comparison of results with those obtained from established laboratory tests in an effort to evaluate the usefulness of the WSN system. While the development of the WSN system is still ongoing by the partners, many sensor types are already supported. This paper presents WSN implementations on the Holy Cross Minster in Schwäbisch Gmünd, Germany, Schönbrunn Castle Chapel in Vienna, Austria, archaic houses in Hebron, Palestine, and Bode Museum in Berlin, Germany. The system design, including hardware and software, sensor types and their characteristics, and their adaptation to the system is described. System setup is described for each case study and results of initial measurements are shown, including smart automatic interpretation mechanisms. An assessment of the wireless monitoring system concludes the paper, stating research needs and future work.