The present paper was prompted by the activity carried out within the scope of an EU-funded project (WARMEST). It calls to analyse the reasons for the degradation of the Patio de Los Leones, which attracts over 2 million tourists per year to Granada in Spain. We review here the most advanced studies and regulations on the assessment of the social impact of mass tourism and present a novel methodology to analyse its effects. We dug into the material available on social networks—especially feedback to posts published on major relevant sites—and got a comprehensive picture of the thoughts that were expressed there and a comprehensive assessment of the citizens’ opinion on the social impact of tourism in Granada. Thus, we obtained a new indicator called “C.1.2 index modified”, which measures the level of dissatisfaction of citizens with the tourists’ pressure; we propose to replace the existing ETIS index with C.1.2, which is mainly based on direct surveys that are often carried out with very limited resources. At the end of the research, we could point out topics that are especially important to the citizens, thus allowing us to define a strategic action plan with a bottom-up approach.