Digital Twins (DTs) represent high potential solutions to answer digital transformation questions in organizations such as companies. DTs could indeed perform monitoring, simulation, computer-aided decision and optimization regarding a given system of interest through a digital system that mirrors this system of interest. In this short paper, we propose a twenty-year retrospective on the DT concept before stating remaining questions. Then, we briefly share our vision of the DT concept in the railway context along with the methods we used to produce our DT as part of our information system at ``SNCF Réseau''.