Cyber-Physical Systems (CPSs) are getting increasingly complex and generate large amounts of data. Analyzing such data provides us an insight into a given system. The digital twin concept emerges as an attempt to seamlessly integrate the data and insight in order to improve system performances. It enables applications such as visualization, monitoring, state estimation, and self-adaptation. In this paper, we demonstrate the construction of a digital twin exemplified by an incubator system, including the benefits and challenges of each application. The result is a description of the building blocks of a digital twin.