For cultural heritage destinations, the key risk of tourism growth is associated not only with limited resources but also with the limited capacity to manage flows in near real time. The article proposes an approach in which digitalization is treated as a sustainability-enhancing factor rather than as a parallel “technological” vector. On this basis, an integral SDT index (Sustainable–Digital Tourism index) with a digital multiplier is developed. The multiplier reflects how digital maturity increases the return on infrastructure and institutional measures by reducing transaction costs, improving transparency, and enhancing demand management.