ABSTRACT Overtourism has become a major challenge for many popular tourist destinations, leading to environmental, social, and cultural degradation. However, the potential benefits and challenges of spill-over tourism, which refers to the redistribution of tourists to secondary or alternative destinations, are not well understood. This study examines the phenomena of overtourism and spillover impact in the renowned Himalayan Mountain Destinations of Darjeeling and Sikkim in India. The ST-DBSCAN technique is employed to examine a collection of geotagged photo information obtained from Flickr. The objective of this research is to identify the most popular tourist spots in a certain area and analyse the patterns of visitor activity over time. To further investigate the travel pattern of the tourists among the clusters, a Markov Chain Model has been constructed. The findings show that spill-over tourism has the potential to distribute tourism flows more evenly reducing the negative impacts of overtourism. However, challenges such as the risk of environmental degradation in secondary destinations, unequal distribution of benefits, and the potential for creating new overtourism hotspots. This study explores the concept of overtourism and proposes the utilisation of tourism spillover zones as a strategy for sustainable tourist development.