This technical paper is a contribution to the identification of current challenges of semantic 3D city models. They are presented in four parts, namely 3D enriched city models and their connection with urban information models and smartcities, urban models integration, urban analyses and data. This work is an output of the COST Action TU0801 "Semantic Enrichment of 3D city models for sustainable urban development".@en

The basic concept of a Digital Twin (DT) is a realistic digital representation of a physical thing with two-way flow of information from the physical to the model and back: one way is a refinement of the digital representation, back is the triggering of real impacts on the depicted reality. This concept was introduced by the manufacturing community to improve product life-cycle. It has extended to the built environment and underpins areas ranging from urban administration to telecommunications. Locationenabled Digital Twins are investigated at city and national levels motivated by cost reduction, efficiency, decision-making and innovation, and particularly to contribute to local and national Net Zero initiatives [Ellul et al. 2022].@en