The aim of the study is to analyze the challenges and opportunities of conversions and adaptations of Polish modernist hotel buildings to new functions. Preliminary research shows that hotels constitute a significant group among unused buildings from that period. This issue remains unexplored, while the market situation shows that investors will increasingly face an economic, social, and environmental dilemma as to demolish existing facilities and replace them with new structures or thoroughly rebuild and reuse. The study was conducted based on an analysis of groups of criteria in terms of the potential and difficulties associated with investments utilizing the existing hotel fabric, taking into account environmental, formal, structural, functional, and socio-cultural aspects. The results of the study show that the conversion or adaptation of modernist hotels in Poland to a new function is primarily determined by technical issues, i.e., the original structural layout and technical condition of the building, and such investments require decisive action, primarily in terms of replacing external partitions and adapting internal communication systems. However, it has been proven that, in many cases, such investments are possible, and they bring a number of environmental and social benefits, so they are at least desirable from the perspective of sustainable development.