Over 300 cities are inscribed on the World Heritage List. While each site has its unique challenges and opportunities, in each of them a balance must be achieved in protecting heritage values and meeting demands of modern life, including the demand for energy efficiency and the reduction of greenhouse gas emissions. This article uses Visby (Sweden) as a case study to examine how conservation laws implementing the World Heritage Convention in light of international commitments to mitigate climate change can influence the balance between cultural heritage preservation and energy measures in historic sites. International laws must be implemented by states. But these national laws must be applied locally, in each heritage site. It is therefore important to examine how regional and local decision makers, including individual property owners, navigate and understand their obligations stemming from international laws in order to understand the impact and challenges in meeting sustainability goals in heritage sites. We find that while Visby’s World Heritage status promotes a high level of cultural heritage protection, restrictive laws alone fall short in achieving sustainability. Supportive factors such as funding, planning tools, knowledge support and dissemination, and community engagement help bridge these gaps. We recommend further support for financial incentives, place-based technological solutions, and collaboration amongst experts and others to help officials and property owners make choices that are sustainable from both energy and heritage perspectives.